Wednesday, December 15, 2010

Intracontinental Tectonics, Stresses, and Fracture Reservoirs - Clues from Plate Kinematics


Now in its sixth decade, plate tectonics has reshaped the understanding of the evolution of the Earth, especially the origin of major earthquakes, ocean basins, mountain belts, and magmatism. Elaboration of the theory relative to hydrocarbon exploration and development has provided insight into the nature of continental margin sedimentary basins, especially in concert with improved understanding of stratigraphic sequencing, fluid pressures and migration, diagenesis, and compaction. Plate tectonics has also provided a framework for understanding compressional thrust belts associated with convergent plate boundaries, both continental to continental and continental to oceanic plate.

Does plate tectonics provide additional insight into intracontinental plate environments, away from either contemporary plate boundaries (such as subduction zones or transform faults) or paleo-plate boundaries (such as passive continental margins which originated as rifts and seafloor spreading centers)? More specifically, for fracture reservoirs, can plate tectonics provide improved predictive ability for paleofracture existence, density, and orientation and contemporary stress field orientation? The increasing sophistication of horizontal drilling technology cannot help but benefit from improved characterization of paleo- and contemporary stress fields. In both mountain belt and continental margin basin environments, the role of in situ stress induced by plate tectonic and gravitational forces is moderately well understood. The nature and role of stress fields and fracturing within continental interiors is less well comprehended.

Within continental interior basins the existence of consistently oriented and measurable in situ stresses has been demonstrated for a number of continents. Further, the orientations have been correlated to a degree with some elements of plate tectonics. Zoback et al. (1989; following previous workers) documented apparent correspondence of contemporary stress indicator orientations in continental interiors with plate motions in the hotspot reference frame for North America and Africa, especially, and possibly western Eurasia and South America. Fig. 1 illustrates this correspondence for North America. From Alberta to central Texas to upstate New York, the contemporary maximum principal horizontal compressive stress (sH1) is predominantly oriented northeast-southwest. And, according the plate hotspot model, at present North American is moving in the same direction relative to the hotspot reference frame (e.g., Gripp and Gordon, 2002). However, elements of plate-hotspot theory remain controversial, and the stress-kinematics correlation is incomplete.
Fig. 1. Contemporary maximum principal horizontal compressive stress orientation (sH1) measurements, North America, together with flowlines of North American plate motion in the Tristan hotspot reference frame calculated from the parameters of Gripp and Gordon (2002). (Click to enlarge.)

Improved understanding of the controls and mechanisms of oriented stresses in continental interiors is of particular interest in hydrocarbon exploration, especially for reservoirs which largely consist of fracture porosity or for reservoirs whose productivity can be enhanced by induced hydrofracturing. Knowledge of the likely age and orientation of paleofractures, whether the fractures are hydrocarbon-filled, and/or the likely orientation of induced fractures is of critical value for exploration and development of fracture reservoirs.

This paper examines the evidence for plate tectonic controls on intracontinental stress fields, not only for the present-day, but in the geological past, extending into the Early Cretaceous. The correspondences described herein may be unfamiliar to many explorationists. The key extension of plate tectonics is the “hotspot” hypothesis of Wilson (1963a,b) and its further elaboration as the fixed plume hypothesis of Morgan (1971, 1972a, 1972b). Plate motions relative to the hotspots (or plumes) appear to be correlated with intracontinental stress orientations. It is this correlation that is explored in greater depth herein.

Lastly, this paper presents a strategy for utilizing the correspondence of plate models and stress fields for fracture reservoir exploration and development. Knowledge of the likely orientation of paleo- and induced fractures from plate-hotspot modeling is not enough. In intracontinental environments, the magnitude of the plate-driven stresses usually has not been great enough produce fracturing. Other mechanisms for naturally induced fracturing is required: (1) rapid basin subsidence and sedimentation with overpressuring or (2) regional uplift and erosion, resulting in lithostatic pressure reduction; in either of these cases, the regional, plate-driven stresses may control the orientation of the fractures, if not the induced fracturing itself. Further, the orientation of the contemporary stress field relative to fractures and the presence or absence of multiple fracture sets may control whether fractures are fluid-filled or void. And, knowledge of the relative orientation of contemporary stresses and fractures can also affect decisions on hydrofracturing approaches in either vertical or horizontal boreholes.


A lively debate on the merits of the hotspot/plume model continues at present, over thirty years since Morgan (1971) first presented it, with a website,, serving as unofficial locus of the debate. The administrators of the website and many of its contributors are plume skeptics, but the website, nevertheless, provide links to contributions from a wide variety of workers, both pro and con.

This contribution does not directly address the viability of the plume hypothesis for the origin of hotspots; its resolution is not essential to the argument advanced here. Rather, a separate component of Morgan’s original hypothesis, fixity of hotspots, is the basis of the analysis presented here. Morgan (1972a) showed that the hotspots he recognized apparently form a globally consistent reference frame at present. Shortly after Morgan produced his first plate-hotspot kinematic model, other workers undertook more exhaustive analysis, with larger data sets, and came to the same conclusion (most recently, Gripp and Gordon, 2002). At present, instantaneous plate motions over inferred hotspots such as Hawaii, Easter, Iceland, Reunion, Tristan da Cunha, Yellowstone, and Kerguelen, as recorded by the traces of the hotspots, imply little relative motion among the hotspots.

Prior to the present, however, it has become apparent that identified hotspots and their traces do not form a single globally-fixed reference frame extending into the geologic past prior to 25 Ma. Rather, the hotspots beneath the Pacific Ocean form one reference frame (from the present to 140 Ma), those beneath the Indian and much of the North and South Atlantic Oceans form another (perhaps to 130 Ma), while a third frame may underlie the northernmost North Atlantic and Arctic Oceans (e.g., Norton, 2000; Raymond et al., 2000, Pilger, 2003, 2007). For convenience, Pilger (2003) has termed the Pacific hotspots the “Hawaiian”, the Indian-Atlantic the “Tristan”, and northernmost Atlantic the “Icelandic” reference frames. In essence, volcanic traces on the oceanic plates imply that the underlying hotspots within each reference frame do not move much relative to one another, while movement between reference frames is significant and measurable, especially prior to 25 Ma. (As an aside, it should be noted further, that “hotspots” might be better termed “melting spots”, if their partially molten state is due to geochemical or temperature heterogeneity in the sub-plate mantle, rather than an anomalously hotter region. The former term is still used in this paper, because of its wide usage; but it should not be inferred to have necessarily genetic implications.)

Plate Kinematics

One of the key advances that facilitated the development and elaboration of plate tectonics was recognition that any motion of a point on the surface of a sphere can be described as a rotation around an axis through the center of the sphere (e.g., Bullard et al., 1965). Intersection of the axis of rotation with the surface of the sphere defines two poles, with spherical coordinates of latitude and longitude. For instantaneous motions, an angular rate of rotation around the pole comprises a third parameter. For finite motions, the angle of rotation is the third parameter. Thus, a reconstruction of Africa and South American before the formation of the South Atlantic Ocean is described by three parameters: latitude and longitude of the pole, and the total rotation angle; either plate can serve as the reference frame for the rotation.

What might be called second generation plate tectonics began in the 1970s. Acquisition of marine magnetic and bathymetric profiles of the ocean basins led to the identification of magnetic isochrons and fracture zones formed at seafloor spreading centers (mid-ocean ridges and rises), from which discrete finite plate reconstructions were calculated. Thus Pitman and Talwani (1972) and Weissel and Hayes (1972) produced respective sets of reconstructions of the North Atlantic (Eurasian, African, and North American plates) and southeast Indian Ocean (Australian and Antarctic plates). As marine data accumulated and was interpreted, it became possible to combine plate reconstructions so as to determine the relative positions of plates which do not share a seafloor spreading boundary. Thus, the relative positions of the North American and Pacific plates at discrete times can be calculated by following the circuit: North American > African > Antarctic > Pacific.

It is a principle of structural geology that knowledge of the initial and final configurations of deformed rock does not uniquely define the deformational path the rock experienced. Similarly, knowledge of finite rotation parameters which describe a plate reconstruction does not require that the poles and rates of rotation remain fixed. Rather, the rotation parameters could, and probably do, vary through time; the most recently completed plate reconstruction sets in the world oceans show little evidence of fixity of plate kinematic parameters through time (e.g., see the compilation of Müller et al., 2008).

In the case of hotspots, plate motions can be calculated by fitting multiple traces to inferred corresponding hotspots for discrete times. Accurate isotopic dating of volcanic samples from the traces (island seamount chains and aseismic ridges) provides a minimum age for the position of the hotspot beneath the trace. For the Tristan hotspot set, Muller et al.’s (1993) plate hotspot model is the current “best-fit,” although an “average” model, assuming significant mantle convection has been more recently produced (O’Neill et al., 2005). A number of recent models for the Hawaiian set have been produced, including Wessel and Kroenke (2006, 2008), Andrews et al. (2007), Raymond et al. (2000, corrected), and Norton (2000). A major change in the two most recent models comes from incorporation of an older age for the “bend” in the Hawaiian-Emperor island-seamount chain from 43 Ma to 48 Ma (Sharp and Clague, 2006). Norton (2000) also provides a preliminary model of plate motions relative to the Icelandic frame.

Suppose that we want to determine the motion of the North American plate relative to the Tristan hotspot frame. The plate-hotspot model of Muller et al. (1993), which is centered on Africa, includes North American-hotspot parameters, which could be used directly. However, subsequent to publication of their model, revisions to the geomagnetic time scale have occurred (e.g., Cande and Kent, 1995; Gradstein et al., 2005), and improved, higher resolution, relative plate reconstruction parameters have been produced (e.g., Muller et al., 2008). For our purposes, then, the (short) plate circuit for North American relative to the Tristan reference frame is North American > African > Tristan, with incorporation of the Gradstein et al. time scale. For the North American relative to Hawaiian reference frame, the (longer) circuit is North American > African > Antarctic > Pacific > Hawaiian, using the hotspot model of Wessel and Kroenke (2008), and the Gradstein et al. time scale. Relative plate reconstructions parameters within both circuits are the same as those used and cited by Pilger (2007), modified for the revised time scale.

Finite reconstruction parameter sequences between plates in a plate circuit may or may not be available for the same ages, as the ages correspond with easily identifiable magnetic isochrons, which vary from ocean to ocean. Thus interpolation of the parameters may be necessary. Interpolation is essential, if reconstructions are to be determined at regular age intervals (e.g., 5 m.y.).

From the earliest second generation reconstruction approaches, interpolation of plate reconstructions and inference of kinematics both have utilized simple finite difference calculations. That is, the “difference” of two total finite reconstructions is most easily calculated as a simple rotation. And, the average angular rate of motion between the two reconstructions is the difference rotation angle divided by the reconstruction age difference. (Aside: composition of rotations requires matrix operations, not simple vector addition or subtraction. Rotation “differences” are not simple algebraic differences.)

The problem with the finite difference approach is that it introduces discontinuities in rate and direction of plate motion which correspond precisely with each reconstruction. Ironically, magnetic isochrons are best identified over oceanic plate that does not show abrupt changes in motion; thus finite difference approaches introduce abrupt changes which almost surely do not exist.

As an alternative to finite difference methods, Pilger (2003) introduced vector cubic spline interpolation of reconstruction parameters. The spline approach results in smooth, continuous changes in both finite and instantaneous rotation parameters and provides a means for calculating the latter, as well.

Plate Kinematics and Stress Indicators

If the correspondence of plate motion and sH1 measurements as in Fig. 1 is real, what might the genesis be? Perhaps there is a more basic question: What is the significance of coherent contemporary intracontinental stress orientations within North America? There is substantial evidence that plate motions are driven by gravitational forces – pull from subduction zones and isostatically driven “sliding” off ridges (e.g., Richardson, 1982; Lithgow-Bertelloni and Richards, 1998). Frictional traction of the moving plates over the underlying deeper mantle (asthenosphere or mesosphere) would then produce compressional stresses oriented parallel to the direction of plate motion relative to the underlying mantle, and coherent stress fields would result within the continental plate interior.

Correspondence of coherent stress fields with plate motion relative to hotspots would further imply that the hotspots are embedded within the upper mantle that is also reflected in the observed stress field orientations. Further, minimal motion of the hotspots relative to one another (forming a reference frame) implies minimal convection within the upper mantle compared with plate motion rates. Is there additional kinematic evidence that hotspots are “embedded” in a slowly convecting upper mantle?

If there is indeed a real correspondence between contemporary stress orientations in continental interiors and plate motions in a hotspot reference, a physical explanation is certainly desirable. However, even in the absence of a convincing physical explanation, an empirical correspondence is still of potential value for prediction of paleostress orientation within continental interiors. Thus, further exploration of the possible correlation of stresses and plate motions is desirable, not only for the present, but also for the geological past.

Stress Indicators

The contemporary stress indicators used by Zoback et al. (1989; and the updated World Stress Project database) include: earthquake focal mechanisms, elliptical borehole breakouts, in situ hydrofracture measurements, quarry pop-ups, aligned Recent volcanic centers, active faults, and Recent joints. Pilger (2003) compiled paleostress orientations from isotopically dated igneous dike and vein sets, age-constrained faults, fractures, and horizontal stylolites for North America, Africa, South America, Western Europe and Australia. North America (principally the United States), Western Europe, and East Africa provided the largest data sets.

Following Zoback et al. (1989), stress indicators are reduced to the orientation of the maximum principal horizontal stress, sigma h-max, or sH1. For quarry pop-ups, sH1 is normal to the strike of the compressional feature (fold and/or thrust fault). Stress orientations for earthquake focal mechanisms are inferred from the solution itself, projected to the horizontal. (For paleostresses, of course, these two classes of observations are irrelevant.) In the case of dikes and veins, extensional fractures and joints, normal faults, and horizontal stylolites, sH1 parallels the strike of each feature.

Hotspots and the Embedding Mantle

In Morgan’s (1971, 1972a,b) original formulation of the plume hypothesis, the relative fixity of the plumes relative to one another, comprising an “absolute” reference frame, did not incorporate any clear characterization of the kinematics and dynamics of the mantle surrounding the plume, other than slow convection. The question, which is particularly relevant to intraplate stress fields, is whether plate versus mantle motion is equivalent to plate versus hotspot motion. The contemporary correspondence of intracontinental stress indicators with plate-to-hotspot kinematics provides a preliminary answer to the question. Are there other indicators of plate mantle motion?

The first candidate that one might imagine records such motion is paleomagnetic measurements. However, neither the Tristan nor the Hawaiian hotspot frames are fixed relative to the paleomagnetic poles as measured from both continental and oceanic analyses (e.g., Morgan, 1981, for the Atlantic-bordering continents and Gordon and Cape, 1981, for the Pacific).

There are, however, three other data sets with associated kinematic reconstructions that provide some indication of plate motion relative to the mantle which may be independent of plumes (or melting spots).

Caribbean Reconstructions

In an analysis of the tectonics of the Caribbean region, Muller et al. (1998) presented reconstructions of the Antillean volcanic island arcs relative to North America (based on studies of Pindell, 1995) and relative to the Atlantic-Indian Ocean (Tristan) hotspot set. Fig. 2 is based on their analysis, using updated reconstruction parameters and timescale.

Figure 2a illustrates the inferred position of the island arc at discrete times relative to North America. Figure 2b illustrates the restored position of the arc to the Tristan frame, using the parameters in Table 1. Note the remarkable correspondence of the restored arcs with each other, from present to ~70 Ma.
Figure 2a. Inferred positions of volcanic centers, Lesser and Greater Antilles Island Arcs relative to North America (after Pindell, 1995), present (red) 9.5 Ma (pink), 19 Ma (orange) 33 Ma (light green), 48 Ma (dark green), 56 Ma (gray-green), 72 Ma (blue).
Figure 2b. Inferred positions of volcanic centers, Lesser and Greater Antilles Island Arcs relative to Tristan hotspot reference frame (this paper). 

The position of the volcanic arc above a subduction zone appears to be controlled by the configuration of the subducting oceanic plate and the zone of contact of the upper surface of the subducting plate with the base of the overriding plate and, therefore, the top of the hot, partially molten asthenosphere (e.g., Cross and Pilger, 1983). For dynamic reasons, it would seem difficult for the channel formed by the subducting slab to displace adjacent mantle in a direction normal to the convergent plate boundary. Therefore, stationarity of the subduction zone relative to surrounding mantle would not be surprising. What is remarkable is the apparent correspondence of the hotspot reference frame with the mantle. This implies that the mantle in which the hotspots are embedded is moving very slowly and forms the same reference frame that the Antillean subduction zone channel is constrained to occupy. Thus both rising regions of the mantle (melting spots or plumes) and sinking regions (subduction zones) are constrained within the same mantle reference frame; therefore the shallow mantle is convecting very slowly.

East African Volcanism

In a second-generation plate tectonic contribution, Turcotte and Oxburgh (1973, 1974) demonstrated apparent time-transgressive onset of volcanism along the East African Rift system. Fig. 2 is a plot of isotopic dates from East Africa, in map view and versus latitude, illustrating the trend they observed. In addition, two predicted loci of motion of the African plate relative to the Tristan hotspot reference frame. Note that the shape of the locus on the left in Fig. 2b envelopes the youngest dates versus latitude. Note also that following onset of magmatism at any particular latitude, the activity has persisted almost to the present. Such a pattern is also observed along the Snake River Plain extending to the southwest and west of Yellowstone in the United States (Fig. 3; Suppe et al., 1975). The pattern could be interpreted to represent movement of Africa over a plume, with subsequent channeling of plume flow to the north, maintaining volcanic activity for tens of millions of years after inception. Alternatively, the pattern may represent propagating rifting from north-to-south as Turcotte and Oxburgh interpreted. If the second interpretation is the case, then, again, there is a correspondence of plate-mantle motion with the hotspot frame semi-independent of plume tectonics. In any case, the volcanic age pattern is inconsistent with the model advanced by Ebinger and Sleep (1998), which ascribes the volcanism to a spreading plume head; their model implies much more rapid propagation of volcanism (faster than African plate motion relative to the hotspot frame) than is observed.

Figure 3a. Isotopic dates (filled diamonds), East African volcanics: age (vertical axis) versus latitude (horizontal axis) with synthetic hotspot traces (open squares) calculated from parameters of Müller et al., (1993).

 Figure 3b. Isotopic dates and synthetic hotspot traces, age versus longitude (horizontal axis) with synthetic hotspot traces as Fig. 3a.

Fig 3c. Map view stereo pair, Isotopic dates and synthetic hotspot traces, as in Fig. 3a,b. (It may be necessary to print out these maps and vary their spacing in order to "see" the stereo effect.)

Fig 3d. Map view stereo pair, "restored" isotopic dates and synthetic hotspot traces using inverse parameters of Müller et al., (1993), to position at time of isotopic cooling ("age"). Compare with Fig. 3c. Note that all but one date is restored to the north of 5˚ south latitude.

East Australian Volcanism

Cenozoic volcanism in the East Australian Highlands evidences a pattern inverse to that in East Africa (Wellman and McDougall, 1973). Fig. 4a illustrates map view of sample locations of isotopic dates of the region and 4b age versus latitude, together with synthetic hotspot trace relative to Tristan hotspot reference frame and the parameters of Müller et al. (1993). Note that a progressive pattern of cessation from north to south is apparent and corresponds with a calculated locus of Australian plate motion relative to the Tristan hotspot frame (e.g., Pilger, 1982). It is not at all apparent how a plume origin for the volcanism can easily account for this termination pattern, especially with persistence of magmatism for as much as 60 m.y. Pilger (1982) suggested a migrating stress node might be responsible, with progressive replacement of an extensional regime with a compressive regime. Very young volcanism in northern Queensland could imply the onset of a new phase of extension. Sutherland (1985) has proposed that the pattern could represent overriding of a paleo-spreading center, although the termination effect is unexplained in his model. In either case, the correspondence of the termination pattern with calculated plate-hotspot frame motions implies, again, stability of the shallow mantle beneath the lithosphere.

Comparing sH1 and Plate-Hotspot Kinematics

Figure 5 consists of maps of United States sH1 measurements in 10 m.y. increments, over the past 80 m.y., together with calculated instantaneous kinematic flowlines of plate motion in the Tristan hotspot frame at 5 m.y. intervals. If plate motions are correlated with intraplate stress, sH1 from continental interiors should parallel the flowlines. Stress measurements from the Mid-to-Late Cenozoic Basin Range and Rio Grande Rift of the western United States and northern Mexico are expected to reflect the pervasive extensional tectonics of the region, while coastal California stresses for the same time period should manifest San Andreas transform tectonics, rather than North American plate motion in the hotspot frame. Further, Laramide and Sevier tectonism are expected to dominate Rocky Mountain and Cordilleran stress fields in the Late Cretaceous and early Cenozoic.
Figure 5a. sH1 measurements from present to 10 Ma, from World Stress Data Center and compilation of Pilger (2003, 2010). 0 to 5 Ma bars in light blue; 5 to 10 Ma in dark blue. Also shown are tangents to instantaneous flowlines for indicated ages (in Ma).

Figure 5b. As Fig. 5a, sH1 10 to 15 Ma bars in light blue; 15 to 20 Ma in dark blue.

 Figure 5c. As Fig. 5a, sH1 20 to 25 Ma bars in light blue; 25 to 30 Ma in dark blue.
 Figure 5d. As Fig. 5a, sH1 30 to 35 Ma bars in light blue; 35 to 40 Ma in dark blue.

 Figure 5e. As Fig. 5a, sH1 40 to 45 Ma bars in light blue; 45 to 50 Ma in dark blue.

Figure 5f. As Fig. 5a, sH1 50 to 55 Ma bars in light blue; 55 to 60 Ma in dark blue.

Figure 5g. As Fig. 5a, sH1 60 to 65 Ma bars in light blue; 65 to 70 Ma in dark blue. 
Figure 5h.  As Fig. 5a, sH1 70 to 75 Ma bars in light blue; 75 to 80 Ma in dark blue.

Figure 6 is a plot of sH1 and kinematic azimuth of North American motion in the Tristan hotspot frame (calculated from the parameters in Table 1, using the instantaneous method of Pilger, 2003) versus age. A fair correspondence, with some dispersion is apparent between 100 to 20 Ma, noting that the onset of extension in the Cordillera is apparent about 40 Ma.
Figure 6. Observed sH1 and kinematic azimuths versus age, United States.d

The time periods and locales in which an apparent correspondence of predicted and observed paleostresses is observed in the figures are as follows:

• 50-75 Ma, Southern Basin Range, Figs. 5f-h.

• 45-50 Ma, Southern Basin Range, central Montana, Fig. 5e.

• 30-45 Ma, Trans-Pecos, Figs. 5d-e.

• 20-35 Ma, Southern Rocky Mountains, Figs. 5c-d.

The absence of obvious correspondence between stress indicators and flowlines since 20 Ma is attributed to the slower rate of calculated North American plate motion relative to earlier periods, the greater importance of Basin-Range and Rio Grande Rift extension beginning about 25 Ma, and lack of exposure of younger dikes by erosion.

Clearly, to imply that a plate-level stress field is the dominant factor in controlling fracture orientation overlooks other potential controls, especially preexisting structures. Further, local stress predictions from plate-scale kinematics must be subject to test in each new area of investigation. More sophisticated finite element modeling of the intracontinental stress field may be required (see, e.g., Dyksterhuis et al., 2005).

Enhanced Fracture Reservoir Exploration Workflow

In what ways can existing contemporary and paleo-stress indicators and tectonic models of regional stress fields be of value in fracture reservoir exploration and development? First, the publicly available contemporary stress data base (World Stress Map: Heidbach et al., 2008) may contain data for the play area. Second, proprietary stress indicator data may exist from borehole breakout analyses or from previous microseismic monitoring from nearby wells.

Fracture analysis of logs from nearby wells can provide insight into the presence of paleofractures, with or without evidence for oil fill. Models of plate tectonic stress field evolution over time, including both orientation and relative magnitude (from plate velocity), can provide additional potential insight into possible paleo-fracture orientation in targeted stratigraphic intervals.

From geohistory analysis of a basin, most probable times of fracturing and maturation may be inferred from decompaction and paleotemperature studies via, for example, density/porosity curves, and vitrinite reflectance, fluid inclusion, and/or oxygen isotope core analysis (e.g., Becker et al., 2010; Olson et al., 2009; Laubach et al., 1995, 2009). The fracture time estimates can then be compared with the predicted plate motion directions as well as with more sophisticated finite element models. Thus, the expected fracture directions can be inferred. Together with structural and stratigraphic models of the basin, the probability that such fractures are oil filled can also be assessed.

If horizontal wells are anticipated, their orientation will then be controlled by either (1) the desire to intersect anticipated (and hydrocarbon filled?) paleofractures and/or (2) the generation of hydrofractures parallel with contemporary sH1 that will access optimal hydrocarbon production with or without preexisting oil-filled paleofractures. Of course, once a successful exploration well is completed, hydrofracturing and associated microseismic surveys, together with production rates and initial declines, provide the subsequent dominant guidance for further development of the field.


Tectonic models of contemporary and past plate motion combined with geohistory analysis provide a preliminary guide to initial exploratory wells and hydrofracturing programs, in the absence of paleo- and contemporary stress indicators for a targeted play,. Once such wells have been successfully completed, the resulting insight into ambient stresses, the presence of hydrocarbon-filled fractures, and production decline rates will guide additional development of the play into the desired economically viable field. And, the resulting information can also provide insight applicable to adjacent areas of potential exploration and development.


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*Paleostress data, sources, and references (Google Docs).

© Rex H. Pilger, Jr., 2010

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