Pressure Transient Analysis in Multilayered Faulted Reservoirs

Sahni, A.; Hatzignatiou, D.G.

doi:10.2523/29674-ms

Cited by 3 publications

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“…By contrast, the effect of a linear boundary, acting either as a constant pressure or as a no-flow boundary, is more persistent, even for linear heterogeneities of non-zero permeability, and changes the slope of fluid pressure evolution with the logarithm of time. This change in the slope of fluid pressure or of its derivative is usually used to detect faults in petroleum engineering (e.g., Gray, 1965;Matthews and Russell, 1967;Earlougher, 1977;Lee, 1982;Sageev et al, 1985;Horne, 1995;Maghsood and Cinco-Ley, 1995;Sahni and Hatzignatiou, 1995;Aydinoglu et al, 2002;Charles et al, 2005).…”

Section: Introductionmentioning

confidence: 99%

A methodology to detect and locate low-permeability faults to reduce the risk of inducing seismicity of fluid injection operations in deep saline formations

Vilarrasa

Bustarret

Laloui

et al. 2017

International Journal of Greenhouse Gas Control

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Fluid injection in the subsurface has significantly increased over the last decades. Since fluid injection causes pressure buildup, reducing effective stresses, shear failure conditions may eventually occur, inducing microseismic and seismic events. Anticipating felt induced earthquakes that may be triggered in undetected faults is crucial for the success of fluid injection projects. We propose a methodology to detect and locate such low-permeability faults to reduce the risk of inducing felt seismic events. The methodology consists in using diagnostic plots to identify the divergence time between the logarithmic derivative of overpressure evolution measured in the field and the one that would correspond to an aquifer including the previously identified heterogeneities. We apply the proposed methodology to water and CO 2 injection through a horizontal well in a confined aquifer that has faults parallel to the well. We numerically obtain type curves that allow locating low-permeability faults once the divergence time is determined from the logarithmic derivative of overpressure for both water and CO 2 injection. Furthermore, we illustrate how to apply the methodology to detect multiple low-permeability faults. To perform a proper pressure management based on fault stability analysis to minimize the risk of inducing felt seismic events, the proposed methodology should be complemented with other multidisciplinary tools. This methodology can be extended to other geological settings and be used in several fluid injection applications.

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Section: Introductionmentioning

confidence: 99%

A methodology to detect and locate low-permeability faults to reduce the risk of inducing seismicity of fluid injection operations in deep saline formations

Vilarrasa

Bustarret

Laloui

et al. 2017

International Journal of Greenhouse Gas Control

View full text Add to dashboard Cite

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Integrating Pressure Transient Test Data with Seismic Attribute Analysis to Characterize an Offshore Fluvial Reservoir

Sahni

Kelsch²,

Samorn

2007

Asia Pacific Oil and Gas Conference and Exhibition

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Interpreting pressure transient tests in complex faulted and stratigraphic environments can be difficult. In fluvial depositional environments, where sand continuity is a significant uncertainty, pressure transient test interpretation can generate several non-unique solutions, all of which may match test data. Using seismic attribute analysis to constrain pressure transient test interpretation leads to better understanding of reservoir heterogeneities and boundaries, and is the central theme of this paper. Additionally, seismic data can guide the design of pressure transient tests, especially the test duration to evaluate key seismic anomalies. Other data such as production history, core data, formation evaluation from well logs, analog information on channel geometry etc. is also important in getting a better understanding of reservoir description. While we briefly discuss all relevant data, the focus of this paper is primarily on integrating seismic amplitude response with pressure transient test interpretation. The interpretation of the pressure transient test is done numerically, guided by an initial interpretation of point bar and channel system geometry from seismic attribute analysis. The analysis of the build-up pressure derivative clearly shows the impact of point bar boundaries and connectivity across point bars. For the reservoir evaluated, there was fluid and pressure communication across the point bars, and this was reflected in the transient pressure analysis of the build-up and also from historical production data. The results presented in this paper illustrate the value of integrating geology, geophysics and production data with well test interpretation for a fluvial reservoir. Introduction The integration of geology with well test interpretation has been discussed by Massaonnat and Bandiziol (1991) and subsequently by Corbett et al. (1998). The latter paper concludes that the integration of geoscience and well testing results in reduction of uncertainty in reservoir description, especially in fluvial reservoirs. Zheng et al. (2003) illustrate this integration using geological, petrophysical, seismic attribute and well test data from a fluvial reservoir in the Gulf of Thailand. More recently, Zheng (2006) concludes that numerical well test interpretation which incorporates reservoir geology and heterogeneity (rock and fluid) is the future of well testing. Raghavan et al. (2000) provide another example of a fluvial gas condensate reservoir where the integration of geologic and geophysical interpretations with measurements from flow tests helped in reservoir characterization. The authors discussed the advantages of using numerical interpretation of well tests as compared to classical analytical interpretation. They also noted that sub seismic features may be identified and their properties estimated by conducting flow tests. Rooij et al. (2002) studied point bar geometry, connectivity and well test signatures in fluvial systems, focusing on the lateral connectivity between point bars. Their work investigated the effect of different types of channel fill sequences on well test signatures and connectivity across channel fills. Toro-Rivera et al. (1994) summarized that flow characteristics of a fluvial reservoir can be better understood by the integrated interpretation of well test pressure data in a geologically coherent fashion.

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Modeling of Complex Geometry Reservoirs

Zhao

Thompson

2000

SPE Annual Technical Conference and Exhibition

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Complex geometry reservoirs can be encountered in the field for variety of depositional and tectonic processes. For example, fluvial depositional environments may produce inter-branching channel reservoirs, or reservoirs consisting of relatively high permeability channels in communication with low-permeability splays. This paper presents a general methodology for computing pressure responses and flow characteristics in complex geometry reservoirs. The proposed method consists of decomposing the original complex-geometry reservoir into a set of simple-geometry reservoirs, which interact with each other by transfer of fluid and equality of pressure over the regions where they are in hydraulic contact. Analytical solutions are written down for each of the simple reservoir components in terms of the unknown pressures and fluxes at their boundaries, and the coupled systems are solved for the desired wellbore pressure responses. The method of sources and sinks is used to compute the pressure response in the Laplace domain and the results are inverted numerically using the Stehfest Inversion algorithm1. We present fast accurate methods of taking numerical Laplace transforms of the source/sink solutions that make the computations reasonably fast and efficient. The proposed methodology can be extended to any system where the Laplace-space solution can be easily written in terms of integrals of real-space source/sink functions, including production at constant bottom-hole pressure, wellbore storage effects or naturally fractured systems. We demonstrate the applicability of the method by modeling branching channels and channel/splay systems. Introduction Classical well test analysis has long been used as a valuable tool in characterizing reservoirs using transient pressure versus time behavior. In most classical well test models, the reservoir is idealized as a "homogeneous" single or dual porosity system with a simple reservoir and well geometry. This is done in order to facilitate generation of analytical solutions to the reservoir problem. In fluvial-deltaic reservoir systems, however, the complex geometry precludes idealizing the reservoir as a simple-shaped homogeneous system and in general, the transient pressure responses do not resemble those of classical simple-geometry systems. Fluvial-deltaic reservoir systems are one example of general complex-geometry reservoirs for which classical well test analysis models may not be applicable. Except for work presented by Larsen2,3 on a network of interconnected linear reservoirs, there appears to have been very little presented in the literature in modeling or describing the pressure transient pressure behavior of these types of reservoirs. Larsen's work was primarily concerned with the long time productivity of a network of intersecting linear reservoirs, with no special consideration given to the geometry at the regions of intersection. Larsen's work indicated that proper understanding of reservoir type is critical in situations where extrapolation of short-time test data to possible late-time production characteristics is attempted. Sealing and/or non-sealing faults have been a major research topic in pressure transient analysis literature. Instead of focusing on the communication between reservoirs, most of the studies have been focused on the effect of the sealing and/or non-sealing faults. Both numerical and analytical solutions have been presented in the literature to model the pressure behavior in faulted reservoirs and some pertinent papers are listed in the references4–9. Modeling Philosophy and Methodology In the following, we illustrate our general modeling approach by applying it to a simple reservoir system. The physical model considered in Fig. 1 consists of two semi-infinite reservoirs separated over most of their extent by a hydraulically sealing barrier. One has flow properties of a "channel", while the other has properties of a "splay". The reservoirs are in hydraulic contact only over a small area. A well is producing from one of the reservoirs.

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Pressure Transient Analysis in Multilayered Faulted Reservoirs

Cited by 3 publications

References 0 publications

A methodology to detect and locate low-permeability faults to reduce the risk of inducing seismicity of fluid injection operations in deep saline formations

A methodology to detect and locate low-permeability faults to reduce the risk of inducing seismicity of fluid injection operations in deep saline formations

Integrating Pressure Transient Test Data with Seismic Attribute Analysis to Characterize an Offshore Fluvial Reservoir

Modeling of Complex Geometry Reservoirs

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