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    Peter Hennings ConocoPhillips Subsur-face Technology, PR2014, 600 N. DairyAshford, Houston, Texas;

    Peter Hennings received his B.S. and M.S. de-grees in geology from Texas A&M UniversityRelationship between fractures,fault zones, stress, and reservoirproductivity in the Suban gasfield, Sumatra, Indonesiaand his Ph.D. in geology from the Universityof Texas. He has held various technical andPeter Hennings, Patricia Allwardt, Pijush Paul,

    supervisory positions in Mobil Research Com-Chris Zahm, Ray Reid Jr., Hugh Alley,Copyright 2012. The American Association of Petroleum Geologists. All rights reserved.

    Manuscript received May 3, 2009; provisional acceptance June 18, 2009; revised manuscripJuly 6, 2011; final acceptance August 16, 2011.DOI:10.1306/08161109084

    AAPG Bulletin, v. 96, no. 4 (April 2012), pp. 753772 753pany, Phillips Petroleum Company, and Conoco-Phillips. His research and application focus inRoland Kirschner, Bob Lee, and Elliott Hough

    these positions includes structure and tectonics,seismic interpretation, reservoir description,geomechanics, and fracture characterization. Heis currently the manager of the Structure andGeomechanics Group in ConocoPhillips Subsur-face Technology. He is an AAPG distinguishedlecturer, a Geological Society of America honor-ary fellow, and is an adjunct professor at theUniversity of Wyoming and consulting professorat Stanford University.

    Patricia Allwardt ConocoPhillipsSubsurface Technology, PR2014, 600 N.Dairy Ashford, Houston, Texas;

    Patricia Allwardt received her B.S. degree inearth and planetary sciences from HarvardUniversity and her Ph.D. in structural geologyand geomechanics from Stanford University.During work on this paper, Tricia was a memberof the Subsurface Technology Organization atConocoPhillips focused primarily on integratingstructural analysis, fracture characterization,and geomechanics into reservoir performance.Tricia is currently working in ConocoPhillipsGulf of Mexico Exploration Group.

    Pijush Paul ConocoPhillips SubsurfaceTechnology, PR2014, 600 N. Dairy Ashford, Hous-ton, Texas;

    Pijush Paul works in the structure and geome-chanics team of ConocoPhillips SubsurfaceTechnology Group in Houston. He leads theABSTRACT

    It is becoming widely recognized that a relationship existsbetween stress, stress heterogeneity, and the permeability ofsubsurface fractures and faults. We present an analysis of theSouth Sumatra Suban gas field, developed mainly in fracturedcarbonate and crystalline basement, where active deformationhas partitioned the reservoir into distinct structural and stressdomains. These domains have differing geomechanical andstructural attributes that control the permeability architectureof the field.

    The field is a composite of Paleogene extensional elementsthat have been modified by Neogene contraction to producebasement-rooted forced folds and neoformed thrusts. Reservoir-scale faults were interpreted in detail along thewestern flank ofthe field and reveal a classic oblique-compressional geometry.

    Bulk reservoir performance is governed by the local stressarchitecture that acts on existing faults and their fracture dam-age zones to alter their permeability and, hence, their access todistributed gas. Reservoir potential is most enhanced in areasthat have large numbers of fractureswith high ratios of shear tonormal stress. This occurs in areas of the field that are in astrike-slip stress style. Comparatively, reservoir potential islower in areas of the field that are in a thrust-fault stress stylewhere fewer fractures with high shear-to-normal stress ratiosexist. Achieving the highest well productivity relies on tappinginto critically stressed faults and their associated fractureteams computational geomechanics program.His other projects focus on providing geome-chanical models of reservoirs for completionand production optimization. He holds a Ph.D. ingeomechanics and an M.S. degree in petroleumengineering from Stanford University, an MTechdegree in applied geophysics from the IndianInstitute of Technology, and a B.S. degree in

    t received

  • geology and physics from St. Xavier College,India.

    Chris Zahm ConocoPhillips SubsurfaceTechnology, PR2014, 600 N. Dairy Ashford,Houston, Texas; present address: University ofTexas, Bureau of Economic Geology, Austin,Texas;

    Chris Zahm received his B.S. degree in geologyfrom the University of Wisconsin, his M.S. degreein geology from the University of Texas atAustin, and his Ph.D. from the Colorado Schoolof Mines. He was employed by ConocoPhillipsSubsurface Technology where he worked on res-ervoir structural geology projects before joiningthe Bureau of Economic Geology at the Uni-versity of Texas at Austin. He is currently a re-search associate as part of the BEG-ReservoirCharacterization Research Laboratory (RCRL)Industrial Associates program and adjunct pro-fessor in Jackson School of Geosciences.

    Ray Reid Jr. ConocoPhillips SubsurfaceTechnology, PR2014, 600 N. Dairy Ashford,Houston, Texas;

    Ray Reid Jr., is a senior petrophysical analystin ConocoPhillips Subsurface Technology. Rayjoined Phillips Petroleum Company in 1979where he supported geophysical acquisition andexploration. In 2003, Ray joined ConocoPhillips.Since 2003, Ray has led the petrophysical imageprocessing and interpretation function forConocoPhillips.

    Hugh Alley ConocoPhillips Indonesia Inc.,Ltd., Jakarta, Indonesia

    Hugh Alley received his B.Sc. and M.Sc. degrees ingeology from the University of Manitoba in 1975and 1982, respectively. He has held various tech-nical and supervisory positions in the Explorationand Development departments of ConocoPhil-lips, Gulf Canada Resources, Maxus Energy, andAmoco. Hugh is currently a principal geologistsupporting unconventional shale oil and shalegas exploration in ConocoPhillips Canada.

    Roland Kirschner ConocoPhillips Indo-nesia Inc., Ltd., Jakarta, Indonesia

    Roland Kirschner is an exploration geologist withConocoPhillips in Perth, Australia. He receivedhis M.S. degree in geology from Louisiana StateUniversity. Since joining Phillips Petroleum in1999, he has held various technical positions withinPhillips and, later, within ConocoPhillips both in

    754 Suban Gas Field, Sumatra, Indonesiadamage zones. Two wellbores have been drilled based on thisconcept, and each shows a three- to seven-fold improvementin flow potential.INTRODUCTION

    The relationship between stress, stress variability, active faults,and the permeability of natural fracture systems in the sub-surface is becoming widely recognized. Barton et al. (1995)presented initial evidence for elevated fluid flow associatedwith potentially active faults in boreholes in crystalline rock.Zoback (2007) expands this discussion to consider faults at avariety of scales in different geologic environments. Tamagawaand Pollard (2008) discuss a fractured basement gas reservoirwhere fracture-controlled well performance is significantly im-pacted by stress fields perturbed by faults. Also, active defor-mation, as manifested in faulting, can significantly alter the re-gional pattern of horizontal stress. Castillo and Zoback (1994)discuss how recent seismic movement along faults changes thelocal stress configuration at the scale of oil field structures insouthern California. Active deformation related to fault move-ment generates fractures and results in local stress-field pertur-bations, both ofwhich affect permeability in the vicinity of faults.The purpose of this article is to present an analysis of subsur-face data from a fractured gas field that strongly reinforces thesethemes and shows how integration of these concepts can beused to assess reservoir potential and drill wells with higherproductivities.GEOLOGIC BACKGROUND

    Suban field is located along the southwestern edge of theSouth Sumatra Basin in south-central Sumatra. The field pro-duces wet gas from compressionally uplifted fractured crys-talline and metamorphic basement and overlying clastic andreefal carbonate rocks (stratigraphic units [SUs] 1, 2, and 3;Figure 1).

    The island of Sumatra owes its present-day complex tec-tonic architecture to northeast-directed oblique subduction ofthe Indo-Australian plate along its southwestern margin. Sig-nificant crustal decoupling and strain partitioning occur alongthis zone with the fore-arc region southwest of the Sumatranfault moving in a northerly direction, along with the subductingIndo-Australian plate (Figure 1) (Milsom, 2005). This obliquelateral movement interacts with the Sunda craton along the

  • domestic and overseas locations. Besides afascination with fractured reservoirs systems, hismain interests focus on the analysis and mod-eling of the sedimentology and stratigraphy ofshallow-water to deep-marine clastic reservoirsystems.

    Bob Lee ConocoPhillips Indonesia Inc., Ltd.,Jakarta, Indonesia

    Bob Y. Q. Lee received his B.S. degree in chemicalengineering from the University of Saskatch-ewan in 1980. He has held reservoir engineeringpositions with various companies includingConocoPhillips Indonesia and is currently withInterOil. His technical interest is to integrateclassical and analytical reservoir engineeringtechniques with the modern-day workflowof reservoir characterization and simulation.

    Elliott Hough ConocoPhillips IndonesiaInc., Ltd., Jakarta, Indonesia

    Elliott Hough received his B.S. degree in me-chanical engineering from Colorado State Univer-sity in 1980. He has held various technical andsupervisory reservoir engineering positions inPhillips Petroleum Company and ConocoPhillips.Elliott is currently a principal reservoir engineer,supporting unconventional shale oil


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