Unproven Plays (A Sand) in Middle Indus Basin

Unproven Plays (A Sand) in Middle Indus Basin

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  1 PAPG – SPEATC 2014 Un-Proven Plays in Middle Indus Basin Kamran Aziz (Kamran.Aziz@omv.com), Aamir Rasheed (Aamir.Rasheed@omv.com), Adnan Zaidi (Syed_Adnan.Zaidi@omv.com) & Adil Azeem (Adil.Azeem@omv.com) OMV (Pakistan) Exploration GmbH OMV (Pakistan) Exploration GmbH Abstract The recent integrated regional sequence stratigraphic study confirmed the long-known interpretation of the early to mid-Cretaceous successions as representing a transition from shallow to deep marine rocks during the progradation of sedimentary wedges. During deposition, the effects of the Kandra palaeo- high were significant with deposits effectively ponding against it as progradation continued to infill accommodation. The main gas fields in this succession are developed in the shallow- marine sands at the top of this wedge. The basinal turbidite sandstones and/or lowstand delta sands have the potential to provide underexplored or new exploration opportunities. Deposition under different 3rd order cycles of sea-level change had a profound influence on the regional development of reservoirs with the main fields occurring in transgressive/regressive sandstones sealed by the overlying shales. This study revealed that sub-regional variations in subsidence occurred across the Middle Indus Basin and had significant influences on sedimentation. This is represented by the creation of smaller depo-centres that either (i) created anomalous thicknesses of shallow- marine rocks or (ii) created deeper basins containing locally preserved turbidites. It is highly likely that the majority of these fairways are fully exploited with the potential for significant petroleum accumulations (to the west of the current fields) being extremely limited. Therefore, it is anticipated that any new reserves in the Middle Indus Basin will be represented in unproven plays. These unproven plays include turbidites & Lowstand deposits. The turbidites occur within or near to the base of the Sembar Formation and as a consequence, reservoir effectiveness represents an intermediate risk due to depth of burial. In addition to this, due to the limited number of well-penetrations, the regional development of these sandstones is yet to be demonstrated. Based on the evaluation of Cretaceous gas plays in the Middle Indus Basin, it is recommended that less time is devoted to exploring the established play as these less likely to have a significant lateral extent to the west. In contrast, some of the deeper plays may have untapped potential e.g. turbidites and low sand deposits. These require more work to reduce the risk associated with them. 1. Introduction: Objective of this article is to highlight the importance of the unproven plays in the future exploration strategy of the Middle Indus Basin. The Middle Indus Basin lies in the Southern Pakistan on the northern side of Lower Indus Basin from the flanks of Jaccobabad – Khairpur high to the Flanks of Mari – Kandhkot high. In general, the study area comprises a relatively steeper south easterly dipping monocline on the eastern flank of Jaccobabad – Khairpur high (Figure-1) intersected by intra-basinal highs and lows [16]. As previously cited by [2], Early to Mid- Cretaceous sandstone bodies are interpreted to be deposited in a depositional environment representing a transition from deep to shallow marine rocks (Figure-2). The main gas fields in this succession are developed in the shallow- marine sandstone. The basinal turbidite sandstones and/or lowstand delta sands have the potential to provide underexplored or new exploration opportunities. By examination of the creaming curve of Middle Indus Basin (Figure-3) it is observed that Lower Goru play has some terraces and steep legs [5]. Two conclusions can be made by comparison of this creaming curve with the world’s mature basins, keeping in view the sequence stratigraphic framework; 1) Initial exploration has focused on TST and HST (with exception of Sawan field, which is a lowstand shelf-edge delta system) [1].
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  2 2) Existing playshave limited or very limited reserves and next steep leg would come from a new play. This analysis has some similarities with the concept that, discoveries in Lowstand system tract usually sit on the last steep leg of the creaming curve [21]. 2. Petroleum System: Sembar is considered to be the primary petroleum source rock for most of the Lower and Middle Indus Basins. Early to Peak Gas maturation of Sembar-Lower Goru Petroleum System in Middle Indus Basin is from Late Cretaceous to Paleocene [12]. Hydrocarbon charge is considered low risk in the area due to the widespread development of mature source rock (Sembar Formation). Vertical migration dominates above the main gas window. To the West of the Middle Indus Basin, longer distance migration is required, which increases the exploration risk (Figure-4). 3. Sequence Stratigraphy: Sequence Stratigraphic scheme and nomenclature used in this framework is based upon the recognition of third order sequences (1-3 Ma) across Arabian Plate in 2001 and 2004 (Figure-5) [6], [18], [19], [20]. This includes studies in the clastic succession of the Black Sea, mixed carbonate clastics of the Eastern Mediterranean and the carbonates of Abu Dhabi. This scheme focuses on the recognition of Maximum Flooding Surfaces (MFS) and Sequence Boundaries (SB) which are demonstrated to occur in other parts of the globe, correlated at biozone level (Resolution ~ 500,000 years, although variable). This scheme is then correlated with the lithostratigraphic units and their nomenclature, which has been conventionally used by different operators in the study area (Figure-6). OMV conventionally subdivides the Lower Goru Formation into 4 intervals; from bottom to top these are the A, B, C, and D Intervals. These contain the main hydrocarbon producing sandstone reservoir units from, and explored for, across the Middle Indus Basin. At the top of each Interval there is a regionally extensive flooding surface recognized in well and seismic data. This attribute allows the easy integration of this scheme with a sequence stratigraphic model. Using the sequence stratigraphic model described by [18], it was possible to subdivide the early and middle Cretaceous rocks into sequences deposited during different cycles of sea-level change. In this instance, unlike other studies in the Middle Indus Basin, this study defines the base of a sequence at a sequence boundary (Figure-7) rather than a maximum flooding surface. Clastic successions of the Sembar and Lower Goru formations rest unconformably on the carbonates of the Chiltan Formation. The top of this limestone forms a prominent seismic marker in the basin and is considered to represent a subaerial unconformity [11]. This Limestone is taken as acoustic marker in order to better understand the sequence stratigraphic relationships of the overlying stratigraphic intervals. Sembar Formation marks the onset of the sedimentation in a deep basin; refer to the height of the clinoforms on seismic cross-section (Figure-8). High sedimentation rates resulted in the progressive infill of this basin by large prograding wedges of sediment that included turbidites deposited in basin floor fan and/or lower slope settings (Figure-8). Generally the sediment input direction is from eastern side (Indian Craton) of the study area. These sandstones in the Sembar Formation represent additional exploration targets. As sedimentation progressed, the deposition of the A Interval represents a transition from an under- to an overfilled state. In general, the A- D Intervals are dominated by shallow-marine to paralic successions. During deposition, local tectonism and eustasy had a profound influence on deposition. Two distinctive patterns in the strata lying above Chiltan limestone can be observed (Figure-8).
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  3 1 - ProgradingWedges, encompassing K40 to K60 Sequences shows that the basin was under filled at the time. These prograding clinoforms would be expected to have basin floor fan and lowstand delta top. An analogue for these rocks is the Lewis Shale of the USA, which contains both basin-floor fan, delta top and shales gas resources within it (Figure-9) [14]. Traditionally, work on these plays has not been extensive and currently no fields are producing from these plays. This article will highlight the mechanism and potential of these plays. 2- Parallel to sub-parallel reflectors, encompassing K70 to K100 sequences, representing shallow marine environment across the basin. Plays in these intervals have been extensively worked upon by different operators in the area especially by OMV [1], [2], [3], [10], [12], [15], & [22]. 4. Unproven Plays:- a. Sembar Turbidite K50 and K60 LST Plays No fields in Middle Indus Basin are currently recognized in this play but is noted that shows do occur in many of the reservoir sandstones. The petroleum system elements for this play are (Figure-6 & 10): ► Reservoirs: K50/K60 LST turbidite sandstones ► Top seal: K50/60 LST slope shales ► Bottom seal: K50/60 LST slope shales, and ► Charge: Sembar Formation. One of the main issues with this play is uncertainty due to the limited number of well penetrations in Middle Indus Basin. It is also likely that some of the turbidite sandstones in this play are buried to a sufficient depth, indicating an intermediate reservoir effectiveness risk for them. If the reservoir is buried below 3000m overburden, in such a scenario, early chlorite coating of the sandstone reservoir becomes very crucial. Referring to Figure-11, after point “B” which is the onset of chemical compaction; quartz cementation takes place; it would significantly hamper the porosity of sandstone reservoirs [4]. In this situation, either early chlorite coating is essential or the grains should be sufficiently rigid to hold the porosity framework, such that the porosity trend would likely follow trend “D”. Also a contributing factor to inhibit porosity reduction can be early hydrocarbon charge. Due to this pore-pressure inhibits the chemical compaction which in turn is very critical for porosity preservation in siliciclastic sedimentary rocks. The sandstones of this play will occur in slope or base of slope successions and are unlikely to occur on the Jacobad-Khairpur paleo-high (Figure-8). The risks associated with this play will only be reduced through the collation of additional data. This would include well or high-resolution seismic data that can better define reservoir presence at depth. Future Additional Work for Play Evaluation ► Additional penetration in the play would be very critical, effectively providing porosity- permeability data from turbidite deposits in Sembar Formation of both the Middle Indus and Lower Indus Basins. The depth- threshold for reservoir cut-off is only loosely defined. During this process, it should also be considered that the Sembar Formation could be over-pressured as it is buried within the gas window. This attribute will allow porosities and fluid flow to be higher than anticipated. ► High resolution sequence stratigraphic interpretation of the Sembar Formations is required to better observe the geometries of potential turbidites and the likely location of stratigraphic pinch-out. An attempt can also be made to define a range of analogue models for comparable turbidite basins that are developed on continental crust from other parts of the World.
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  4 b. Intra-A SandK60 Lowstand Delta Play No fields are known in this play but significant prospects may occur within it (Figure-8). Shows are recognized throughout the extent of the play. The petroleum system elements are (Figure- 6); ► Reservoirs: K60 LSD sandstones ► Top seal: K60 TST shales ► Bottom seal: K60 slope to lowstand delta shales ► Charge: Sembar Formation. The Maximum thickness of the K60 Lowstand wedge (LSW) is generally in the mid-western part of the study area. The strike of this deposit is generally North-South, while it thins towards the Kandra paleo-high. This deposit thickens towards the north along strike, suggesting greater accommodation and sediment dispersal in that direction (Figure-12 & 13). In this play, three of the petroleum system elements interact to limit its extent. Reservoir risks increase to the west towards the edge of the K60 LST. Due to the sand-prone nature of the A Interval, top seal will tend to be an intermediate risk over most of this basin (the risk would decrease towards west), whilst bottom seals are only developed in the region between the K60 SB and MRS (Figure-7). Future Additional Work for Play Evaluation ► Additional penetrations would add value and help delineate the nature of the transition into lower quality reservoir towards the west. Also this will help to define the extension of the Top and Bottom Seals towards west. ► If high resolution seismic data is acquired, it will add value to the interpretation, especially towards west of the study area. ► High resolution sequence stratigraphic seismic correlation of the depo-centre into which the K60 Lowstand Delta progrades. Risks Associated with Unproven Plays & Recent Well Results a. Sembar Turbidite K50 and K60 LST Plays Major risk associated with Sembar Turbidite K50 and K60 LST Plays is the presence of effective reservoir. These reservoirs are found near the base of slope succession and throughout the Middle Indus Basin, they are found fairly deep. Consequently, burial diagenesis which hampers the permeability of reservoir is a major risk for this play. b. Intra-A Sand K60 Lowstand Delta Play Major Risk associated with Intra-A sand of K60 Lowstand Delta play is the presence of effective top seal which can be provided by K60 TST. The reservoir separation from overlying K60 HST deposits seems to be the major risk for this play. c. Recent Well Results Recently, OMV has tested both these plays in one of the wildcat exploration well as secondary and tertiary targets. Sembar turbidites of K60 LST (tertiary target) were found tight. However, the well location itself was not ideal for testing this play as this may be at tail of the turbidite lobe and was also found at fairly large depth >3500m. Moreover, in order to test these sands at an ideal location, detailed mapping of Lowstand fan has to be carried-out separately. Intra-A sand of K60 Lowstand Delta play was also tested (secondary target), which proved the presence of a thick K60 TST deposit above the reservoir sands, which provided an effective top seal. However, reservoir quality is low at well location, which can be attributed to distal position of the delta. The proximal part may exhibit good reservoir quality sand. In order to mitigate the reservoir effectiveness risk,
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  5 additional reservoir studiesand sequence stratigraphic interpretation needs to be carried out in detail. 5. Conclusions and Recommendations After seismic sequence stratigraphic analysis of early to mid-Cretaceous intervals in Middle Indus Basin, Pakistan, it is concluded and recommended that: 1. K70 to K100 sequence stratigraphic intervals, containing most of the fields in Middle Indus Basin. Only limited potential for significant petroleum accumulations occur to the west of the current fields. 2. K40 to K60 sequence stratigraphic intervals are under-explored and un-proven. So next steep leg in the creaming curve of Lower Goru can be expected from plays within these intervals, which might add significant reserves. 3. The K50 or K60 turbidite sandstones play occurs within, or near to the base, of the Sembar Formation and as a consequence, reservoir effectiveness represents an intermediate risk due to depth of burial. Regional development of these sandstones has yet to be reasonably demonstrated. Further information, reservoir presence is considered an uncertain but intermediate risk. 4. The K60 Lowstand Delta Play is limited by reservoir presence with the notable addition of a top seal risk. Reservoir presence improves to the east, whilst top-seal development improves in the opposite direction. 5. K60 Lowstand Wedge has significant thickness in the mid-western part of the study area. It poses a very attractive exploration opportunity and needs more work at prospect level. 6. High resolution seismic sequence stratigraphic interpretation is required in order to properly delineate unproven plays at prospect scale. 6. References [1] Afzal, J., Kuffner, T., Rahman, A., Ibrahim, M [2009]. Seismic and well-log based sequence stratigraphy of the early Cretaceous, Lower Goru “C” sand of the Sawan gas field, Middle Indus Platform, Pakistan. AAPG Search and Discovery Article # 90139. [2] Ahmad, N, Fink, P., Sturrock, S., Mahmood, T and Ibrahim, M [2004]. Sequence stratigraphy as a predictive tool in Lower Goru Fairway, Lower and Middle Indus Platform, Pakistan. AAPG Search and Discovery Article #10404 [3] Ahmed, A.R. and Ibrahim, M [2008]. 3D modeling of reservoir classes using seismic acoustic impedance data. AAPG Search and Discovery Article # 90151. [4] Ajdukiewicz, J.M and Lander, R.H [2010]. Sandstone reservoir quality prediction: The state of the art. AAPG Bulletin, v. 94, no. 8 (August 2010), p.1083-1091. [5] Daud, F., Khan, G.N., Ibrahim, M [2011]. Remaining hydrocarbon potential in Pakistan. A statistical review. AAPG Search and Discovery Article # 90138. [6] Davies, R.B., Casey, D.M., Horbury, A.D., Sharland, P.R and Simmons M.D. [2002]. Early to mid-Cretaceous mixed carbonate-clastic shelfal systems: examples, issues and models from the Arabian Plate. GeoArabia, v. 7, no. 3, p.541-598. [7] Gradstein, F.M. and Ogg J.G [2004]. Geologic Time Scale 2004 – why, how, and where next! Lethaia, v. 37, p. 175-181. [8] Gradstein, F.M., Ogg, J.G. and Smith, A.G. (Eds.) [2004]. Geologic Time Scale 2004. Cambridge University Press, p.500.
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  6 [9] I.E.D.S., [1995],a sequence stratigraphic study of the Lower Goru – Sembar formations of Lower and Middle Indus Basins of Pakistan and Rajasthan: Multiclient Study. [10] Ibrahim, M [2007]. Seismic inversion data, a tool for reservoir characterization/modeling Sawan gas field – A case study. AAPG Search and Discovery Article # 90140. [11] Iqbal, M, Nazeer, A., Ahmad, H and Murtaza, G [2012]. Hydrocarbon exploration perspective in Middle Jurassic-Early Cretaceous reservoirs in the Sulaiman Fold Belt, Pakistan. AAPG Search and Discovery Article #10394. [12] Krois, P., Mahmood, T and Milan, G [1998]. Miano field, Pakistan, A case history of model driven exploration. AAPG Search and Discovery Article # 90145. [13] OMV internal, Basin Analysis Study – Unpublished. [14] Pyles, D.R and Slatt, R.M [2008]. Stratigraphy of the Lewis shale, Wyoming, USA: Application to understanding shelf-edge to base-of-slope changes in stratigraphic architecture of prograding basin margins. The American Association of Petroleum Geologists – Studies in Geology 56, p.485-489. [15] Rahman, A and Ibrahim, M [2009]. Uncertainty analysis in the Sawan static reservoir model and optimization of facies using neural network technology. AAPG Search and Discovery Article # 90139. [16] Raza, H.A., Ahmed, R., Ali, S.M., Sheikh, A.M., and Shafique, N.A. [1989]. Exploration performance in sedimentary zones of Pakistan. Pakistan Journal of Hydrocarbon Research v.1(1): p.1-7. [17] Reynolds, M. W., 1976, Influence of recurrent Laramide structural growth on sedimentation and petroleum accumulation, Lost Soldier Area, Wyoming: AAPG Bulletin, v. 60, p. 12-33. [18] Sharland, P.R., Archer, R., Casey, D.M., Davies, R.B., Hall, S.H., Heward, A.P., Horbury, A.D and Simmons M.D. [2001]. Arabian Plate Sequence Stratigraphy. GeoArabia Special Publication 2, Gulf PetroLink, Bahrain, p.371. [19] Sharland, P.R., Casey, D.M., Davies, R.B., Simmons, M.D and Sutcliffe, O.E [2004]. Arabian Plate Sequence Stratigraphy – revisions to SP2. GeoArabia, v. 9, no. 1, p. 199- 214. [20] Simmons, M.D., Sharland, P.R., Casey, D.M., Davies, R.B., Sutcliffe, O.E [2007]. Arabian Plate sequence stratigraphy: Potential implications for global chronostratigraphy. GeoArabia, v. 12, no. 4, p.101-104. [21] Snedden, J.W., Sarg, J.F and Ying, X [2003]. Exploration play analysis from a sequence stratigraphic perspective: AAPG Search and Discovery Article #40079. [22] Sultan, S and Ilyas, A [2010]. New stratigraphic play identified in the lower Cretaceous sequence of Middle Indus Basin, Pakistan. AAPG Search and Discovery Articcle # 90120
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  7 Figure-1. Structural Settingof Middle Indus Basin, Pakistan Figure-2. Sequence stratigraphy and play summary chart of the Sembar and Lower Goru sequences, along with the stratigraphic nomenclature used in the industry [2] Study Area
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  8 Figure-3. Creaming curvefor Middle Indus Basin. Each hash represents number of exploration wells drilled [5] Middle Indus Basin - Creaming Curve 0.00 500.00 1000.00 1500.00 2000.00 2500.00 3000.00 3500.00 1925 1928 1931 1934 1937 1940 1943 1946 1949 1952 1955 1958 1961 1964 1967 1970 1973 1976 1979 1982 1985 1988 1991 1994 1997 2000 2003 2006 2009 Cummulative Mari Kandhkot Kadanwari Qadirpur Kandra Miano Block 22 SML discoveries Mari Deep Sawan L. Goru & SML discoveries Major discoveries in Tertiary Carbonates Lower Goru Sandstone discoveries Limited seismic coverage, discovered on highs Dense seismic, stratigraphic and combination traps, Reserves - MMBOE Middle Indus Basin - Creaming Curve 0.00 500.00 1000.00 1500.00 2000.00 2500.00 3000.00 3500.00 1925 1928 1931 1934 1937 1940 1943 1946 1949 1952 1955 1958 1961 1964 1967 1970 1973 1976 1979 1982 1985 1988 1991 1994 1997 2000 2003 2006 2009 Cummulative Mari Kandhkot Kadanwari Qadirpur Kandra Miano Block 22 SML discoveries Mari Deep Sawan L. Goru & SML discoveries Major discoveries in Tertiary Carbonates Lower Goru Sandstone discoveries Limited seismic coverage, discovered on highs Dense seismic, stratigraphic and combination traps, Reserves - MMBOE
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  9 Figure-4. Sembar SourcePotential Map (Colors showing the chance of adequacy, Green being the highest and Red being Lowest)
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  10 Figure-5. Geological TimeScale 2004 [7] & [8]. The Arabian Plate Sequence Stratigraphic Model [18] & [19] is plotted against this timescale
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  11 Figure-6. Nomenclature usedby different Operators and Regional studies in the Study Area. Comparison with Global Sequence Stratigraphic Scheme proposed by [9] & [18].
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  12 Figure-7. Stratigraphic developmentof the early to mid-Cretaceous of Middle Indus Basin
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  13 Figure-8. Seismic SequenceStratigraphic Interpretation of the early to mid-Cretaceous of Middle Indus Basin. Seismic cross-section oriented in regional depositional dip
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  14 Figure-9. Regional dip-orientedstratigraphic cross section of the Lewis Shale and adjacent formations, [14] & [17].
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  15 Figure-10. Regional dip-orientedChrono-stratigraphic cross section of early to mid-Cretaceous Stratigraphic intervals of Middle Indus Basin.
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  16 Figure-11. Porosity-depth trends.Shown is a modeled porosity evolution with burial for well-sorted, fine-grained, quartzo-feldspathic (rigid-grained) sandstone with variable grain coats formed near the surface [4]
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  17 Figure-12. Isochron Mapof the K60 Lowstand Wedge (LSW)
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  18 Figure-13. Seismic cross-section,passing through middle of the study area showing K60 LSW
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  19 Mr. Kamran Aziz Kamranreceived his B.Sc. (Hons) & M.Sc. degrees in Geology from the University of Karachi in 1996 & 1997 respectively. He has also obtained another M.Sc. degree in Petroleum Geoscience with distinction from Oxford Brookes University, Oxford, UK in 2002. He joined OMV (Pakistan) Exploration G.m.b.H in May 2010 and currently working as Lead Geologist in their Exploration Department. In OMV (Pakistan), he is leading the Fold Belt & New Ventures Team since September 2012 and responsible for all G&G activities in Operated/Non-Operated Assets. Before that he was leading the Middle Indus Ventures Team. Previously, he worked for Pakistan Petroleum Limited (PPL) from October 1998 to May 2010 (12 years) at different technical/management positions and was Deputy Chief Geologist in their Exploration Department at the time of leaving the company. His main interests are play fairway analysis using the sequence stratigraphic tool, lead to prospect generation, re-evaluation of remaining block prospectivity, near field exploration, formation evaluation, evaluation of new ventures opportunities and new acquisition. He is an active member of AAPG and PAPG since 2001 and 1998 respectively. Mr. M. Aamir Rasheed Aamir is a Geophysicist by profession. He did his M.Sc. in Geophysics from Quaid-i-Azam University, Islamabad in 2000. He also holds the B.Sc. (Hons) degree in Applied Geology from University of Punjab (1998) with distinction. He started his professional career with BP Pakistan as a Trainee Geophysicist in 2000. During his plus eight years association with BP Pakistan, he remained actively involved in all E&P activities of the company from seismic acquisition till prospect generation/evaluation. Since late 2008, he has been with OMV Pakistan & currently working as a Senior Geophysicist, mainly responsible for G&G activities / studies and prospect evaluation of all operated ventures of Middle Indus Basin. He takes keen interest in Reservoir Characterization through seismic with the state of the art technologies like seismic inversion, special attributes interpretation, and seismic forward modeling. He is an active member of AAPG, SEG and PAPG. Mr. Syed Adnan Haider Zaidi Syed Adnan Haider Zaidi is a Geologist by profession. He did his M.Sc. in Geology in 2003 from the University of the Punjab with major in Petroleum and Structural Geology. He started his professional career with OGDCL, Pakistan in April 2004 and then joined OMV (Pakistan) in February 2012. Currently he is working on OMV operated Middle Indus Ventures. He is involved in Petroleum Systems Evaluation, Play Fairway Analysis and Prospect Generation. He has special interest in Integrated Sedimentology and Sequence Stratigraphy. Mr. Adil Azeem Adil is a Geophysicist in OMV (Pakistan). He did his M.Sc (Geophysics) from Quaid-i-Azam University Islamabad with distinction in 2010. He started his career with Ocean Petroleum Limited as a Trainee Geophysicist. Since Mid-2011, he has been associated with OMV, actively involved in a wide range of E&P projects. Mainly focusing on prospect generation/evaluation in very challenging Middle Indus Basin operated ventures. His professional interests include Seismic sequence stratigraphy, Forward seismic modeling and quantitative seismic interpretation.