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[[file:M114CH03FG01.jpg|300px|thumb|{{figure number|1}}Location of the Barmer Basin in the context of the onshore sedimentary basins in northwestern [[India]] displayed on a map of depth to top [[basement]] (red is shallow, blue is deep; color scales are generalized to reflect deep versus shallow depths to top of basement derived from [[Gravity data|gravity]], [[Magnetic data|magnetic]], and [[Well data|well data]]; based on Dolson et al., 2015<ref name=Dolsonetal2015>Dolson, J. D., S. D. Burley, V. R. Sunder, V. Kothari, B. N. Naidu., N. P. Whiteley, et al., 2015, The discovery petroleum geology of the Barmer Basin, Rajasthan, India: AAPG Bulletin, v. 99, p. 433–465.</ref>). Data points show the distribution of discovered fields in the Barmer and [[Cambay basin]]s and their relative phase ratios of [[gas]], [[oil]], and [[condensate]].]]

[[file:M114CH03FG01.jpg|300px|thumb|{{figure number|1}}Location of the Barmer Basin in the context of the onshore sedimentary basins in northwestern [[India]] displayed on a map of depth to top [[basement]] (red is shallow, blue is deep; color scales are generalized to reflect deep versus shallow depths to top of basement derived from [[Gravity data|gravity]], [[Magnetic data|magnetic]], and [[Well data|well data]]; based on Dolson et al., 2015<ref name=Dolsonetal2015>Dolson, J. D., S. D. Burley, V. R. Sunder, V. Kothari, B. N. Naidu., N. P. Whiteley, et al., 2015, The discovery petroleum geology of the Barmer Basin, Rajasthan, India: [http://http://archives.datapages.com/data/bulletns/2015/03mar/BLTN14045/BLTN14045.html AAPG Bulletin], v. 99, p. 433–465.</ref>). Data points show the distribution of discovered fields in the Barmer and [[Cambay basin]]s and their relative phase ratios of [[gas]], [[oil]], and [[condensate]].]]

==Introduction==

==Introduction==

The Barmer Basin of northwestern Rajasthan, India ([[:file:M114CH03FG01.jpg|Figure 1]]), contains some 7 BBOE (billion barrels oil equivalent) of proven gross in place resources standard tank oil initially in place (STOIIP) in 38 discovered fields and over 3 BBOE of prospective resources in un-drilled leads and prospects. It is a relatively new [[hydrocarbon]] province successfully explored only over the last 20 years (Sisodia and Singh, 2000<ref name=Sisodiaandsingh2000>Sisodia, M.S., and U. K. Singh, 2000, Depositional environment and hydrocarbon prospects of the Barmer Basin, Rajasthan, India: Nafta, Zagreb (Croatia), v. 51, p. 309–326.</ref>; Compton, 2009<ref name=Compton2009>Compton, P. M., 2009, The geology of the Barmer Basin, Rajasthan, India, and the origins of its major oil reservoir, the Fatehgarh Formation: Petroleum Geoscience, v. 15, p. 117–130.</ref>; Dolson et al., 2015<ref name=Dolsonetal2015 />). Sediment thickness exceeds 6 km (4 mi) in the main [[depocenter]]s, but only the main structures in the shallowest 4 km (2.5 mi) of the basin have so far been drilled. The basin is now penetrated by almost 300 exploration and appraisal wells with a success rate of over 50%. Despite this exploration activity, the Barmer Basin remains a relatively underexplored province, certainly when compared with the mature [[Cambay basin|Cambay Basin]] immediately to the south (Biswas, 1987<ref name=Biswas1987>Biswas, S. K., 1987, Regional tectonic framework, structure and evolution of the western marginal basins of India: Tectonophysics, v. 135, p. 307–327.</ref>; Banerjee and Rao, 1993<ref name=Banerjeeandrao1993>Banerjee, A., and K. I. N. Rao, 1993, Geochemical evaluation of part of the Cambay Basin, India. AAPG Bulletin, v. 77, p. 29–48.</ref>; Banerjee et al., 2002<ref name=Banerjeeetal2002>Banerjee, A., S. Pahari, M. Jha, A. K. Sinha, A. K. Jain, N. Kumar, et al., 2002, The effective source rocks in the Cambay basin, India: AAPG Bulletin, v. 86, p. 433–456.</ref>; [[:file:M114CH03FG01.jpg|Figure 1]]). Significant exploration potential remains in deeper structural plays and in post-rift [[stratigraphic trap]]s (Kothari et al., 2015<ref name=Kotharietal2015>Kothari, V., B. N. Naidu, V. R. Sunder, J. D. Dolson, S. D. Burley, N. P. Whiteley, et al., 2015, Discovery and petroleum system of the Barmer Basin, India: [http://searchanddiscovery.com/pdfz/documents/2012/10448naidu/ndx_naidu.pdf.html AAPG Search and Discovery article #110202], accessed November 9, 2016</ref>).

The Barmer Basin of northwestern Rajasthan, India ([[:file:M114CH03FG01.jpg|Figure 1]]), contains some 7 BBOE (billion barrels oil equivalent) of proven gross in place resources standard tank oil initially in place (STOIIP) in 38 discovered fields and over 3 BBOE of prospective resources in un-drilled leads and prospects. It is a relatively new [[hydrocarbon]] province successfully explored only over the last 20 years (Sisodia and Singh, 2000<ref name=Sisodiaandsingh2000>Sisodia, M.S., and U. K. Singh, 2000, Depositional environment and hydrocarbon prospects of the Barmer Basin, Rajasthan, India: Nafta, Zagreb (Croatia), v. 51, p. 309–326.</ref>; Compton, 2009<ref name=Compton2009>Compton, P. M., 2009, The geology of the Barmer Basin, Rajasthan, India, and the origins of its major oil reservoir, the Fatehgarh Formation: Petroleum Geoscience, v. 15, p. 117–130.</ref>; Dolson et al., 2015<ref name=Dolsonetal2015 />). Sediment thickness exceeds 6 km (4 mi) in the main [[depocenter]]s, but only the main structures in the shallowest 4 km (2.5 mi) of the basin have so far been drilled. The basin is now penetrated by almost 300 exploration and appraisal wells with a success rate of over 50%. Despite this exploration activity, the Barmer Basin remains a relatively underexplored province, certainly when compared with the mature [[Cambay basin|Cambay Basin]] immediately to the south (Biswas, 1987<ref name=Biswas1987>Biswas, S. K., 1987, Regional tectonic framework, structure and evolution of the western marginal basins of India: Tectonophysics, v. 135, p. 307–327.</ref>; Banerjee and Rao, 1993<ref name=Banerjeeandrao1993>Banerjee, A., and K. I. N. Rao, 1993, Geochemical evaluation of part of the Cambay Basin, India: [http://http://archives.datapages.com/data/bulletns/1992-93/data/pg/0077/0001/0000/0029.htm AAPG Bulletin], v. 77, p. 29–48.</ref>; Banerjee et al., 2002<ref name=Banerjeeetal2002>Banerjee, A., S. Pahari, M. Jha, A. K. Sinha, A. K. Jain, N. Kumar, et al., 2002, The effective source rocks in the Cambay basin, India: [http://http://archives.datapages.com/data/bulletns/2002/03mar/0433/0433.htm AAPG Bulletin], v. 86, p. 433–456.</ref>; [[:file:M114CH03FG01.jpg|Figure 1]]). Significant exploration potential remains in deeper structural plays and in post-rift [[stratigraphic trap]]s (Kothari et al., 2015<ref name=Kotharietal2015>Kothari, V., B. N. Naidu, V. R. Sunder, J. D. Dolson, S. D. Burley, N. P. Whiteley, et al., 2015, Discovery and petroleum system of the Barmer Basin, India: [http://searchanddiscovery.com/pdfz/documents/2012/10448naidu/ndx_naidu.pdf.html AAPG Search and Discovery article #110202], accessed November 9, 2016</ref>).

An extensive database on [[source rock]] properties, [[heat flow]], [[reservoir]] types, and [[seal rock]] properties has been collected from exploration and appraisal wells together with data from scattered outcrops around the basin flanks and along the northern, uplifted [[Basin margin|margin]] of the basin. A summary of the current understanding of the petroleum geology of the basin is given in Dolson et al. (2015<ref name=Dolsonetal2015 />), while Farrimond et al. (2015)<ref name=Farrimondetal2015>Farrimond, P., B. S. Naidu, S. D. Burley, J. D. Dolson, N. J. Whiteley, and V. Kothari, 2015, Geochemical characterization of oils and their source rocks in the Barmer Basin, Rajasthan, India: Petroleum Geoscience, v. 21, p. 301–321.</ref> detail the aspects of the main source rocks and their properties. The [http://archives.datapages.com/data/specpubs/memoir114/data/61_aapg-sp2030061.htm full paper] associated with this Wiki article describes the construction of, and simulation results from, a pseudo-3-D [[petroleum system]] model calibrated to known [[hydrocarbon]] discoveries and shows. The model has been used to investigate the distribution of discovered [[Oil field|oil]] and [[gas field]]s in the Barmer Basin, the evolution of [[Migration pathway|migration pathway]]s, and the hydrocarbon charge history of the basin as it developed.

An extensive database on [[source rock]] properties, [[heat flow]], [[reservoir]] types, and [[seal rock]] properties has been collected from exploration and appraisal wells together with data from scattered outcrops around the basin flanks and along the northern, uplifted [[Basin margin|margin]] of the basin. A summary of the current understanding of the petroleum geology of the basin is given in Dolson et al. (2015<ref name=Dolsonetal2015 />), while Farrimond et al. (2015)<ref name=Farrimondetal2015>Farrimond, P., B. S. Naidu, S. D. Burley, J. D. Dolson, N. J. Whiteley, and V. Kothari, 2015, Geochemical characterization of oils and their source rocks in the Barmer Basin, Rajasthan, India: Petroleum Geoscience, v. 21, p. 301–321.</ref> detail the aspects of the main source rocks and their properties. The [http://archives.datapages.com/data/specpubs/memoir114/data/61_aapg-sp2030061.htm full paper] associated with this Wiki article describes the construction of, and simulation results from, a pseudo-3-D [[petroleum system]] model calibrated to known [[hydrocarbon]] discoveries and shows. The model has been used to investigate the distribution of discovered [[Oil field|oil]] and [[gas field]]s in the Barmer Basin, the evolution of [[Migration pathway|migration pathway]]s, and the hydrocarbon charge history of the basin as it developed.

==Petroleum Geology==

==Petroleum Geology==

The Barmer Basin is a long (200 km [125 mi]) and narrow (<40 km [<25 mi]) asymmetric [[rift]] that extends broadly north-south in the Thar Desert of western Rajasthan, in northwest India (Figure 1). The basin connects to the north across the buried Devikot High (Siddique, 1963) into the Jaisalmer Basin and to the south to the better-known Cambay Basin via the Sanchor sub-Basin (Kaila et al., 1990; Bladon et al., 2015a; Dolson et al., 2015). Both of these southerly basins are structurally related and comparable to the Barmer Basin in terms of being formed as early Cretaceous to Paleogene rifts, the former of which contains prolific hydrocarbon resources in a sequence of up to 4 km (2 mi) of Paleocene sediments (Biswas, 1982, 1987; Banerjee and Rao, 1993; Gombos et al., 1995). Recent studies indicate that the Barmer Basin is underlain by a poorly known earlier rift of probable Jurassic and certainly Cretaceous age (Bladon et al., 2015a, b; Dolson et al., 2015), which most likely connected to the marine Mesozoic sequences of the Jaisalmer Basin to the north (Singh et al., 2005) and possibly to those of the Kutch and Saurasthra basins to the west (see Figure 1). This deeper Mesozoic basin remains relatively poorly known and underexplored.

The Barmer Basin is a long (200 km [125 mi]) and narrow (<40 km [<25 mi]) asymmetric [[rift]] that extends broadly north-south in the Thar Desert of western Rajasthan, in northwest India ([[:file:M114CH03FG01.jpg|Figure 1]]). The basin connects to the north across the buried [[Devikot High]] (Siddique, 1963<ref name=Siddique1963>Siddique, H. N., 1963, The Jodhpur-Malani divide separating the Barmer and Jaisalmer basins: Journal of the Geological Society of India, v. 4, p. 97–108.</ref>) into the [[Jaisalmer Basin]] and to the south to the better-known [[Cambay Basin]] via the [[Sanchor sub-Basin]] (Kaila et al., 1990<ref name=Kailaetal1990>Kaila, K. L., H. C. Tewari, V. G. Krishna, M. M. Dixit, D. Sarker, and M. S. Reddy, 1990, Deep seismic sounding studies in the north Cambay and Sanchor basins, India: Geophysical Journal International, v. 103, p. 621–637.</ref>; Bladon et al., 2015<ref name=Bladonetal2015a>Bladon, A., S. M. Clarke, and S. D. Burley, 2015, Complex rift geometries resulting from inheritance of pre-existing structures: Insights from the Barmer Basin rift and their regional implications: Journal of Structural Geology, v. 71, p. 136–154.</ref>; Dolson et al., 2015<ref name=Dolsonetal2015 />). Both of these southerly basins are structurally related and comparable to the Barmer Basin in terms of being formed as early [[Cretaceous]] to [[Paleogene]] [[rift]]s, the former of which contains prolific [[hydrocarbon]] resources in a sequence of up to 4 km (2 mi) of [[Paleocene]] [[sediment]]s (Biswas, 1982<ref name=Biswas1982>Biswas, S. K., 1982, Rift Basins in Western Margin of India and their Hydrocarbon Prospects with special reference to Kutch Basin: [http://http://archives.datapages.com/data/bulletns/1982-83/data/pg/0066/0010/1450/1497.htm AAPG Bulletin], v. 66, p. 1497–1513.</ref>, 1987; Banerjee and Rao, 1993<ref name=Banerjeeandrao1993 />; Gombos et al., 1995<ref name=Gombosetal1995>Gombos, A. M., W. G. Powell, and I. O. Norton, 1995, The tectonic evolution of western India and its impact on hydrocarbon occurrences: An overview: Sedimentary Geology, v. 96, p. 119–129.</ref>). Recent studies indicate that the Barmer Basin is underlain by a poorly known earlier [[rift]] of probable [[Jurassic]] and certainly [[Cretaceous]] age (Bladon et al., 2015<ref name=Bladonetal2015a />, 2015<ref name=Bladonetal2015b>Bladon, A., S. M. Clarke, S. D. Burley, and H. Beaumont, 2015, Geology of the Sarnoo Hills, eastern rift-margin of the Barmer Basin, NW India: Basin Research, v. 27, p. 636–655.</ref>; Dolson et al., 2015<ref name=Dolsonetal2015 />), which most likely connected to the marine [[Mesozoic]] sequences of the [[Jaisalmer Basin]] to the north (Singh et al., 2005<ref name=Singhetal2005>Singh, A. K., J. R. Sethi, A. K. Rai, S. Kumar, J. Kundu, and S. M. Goel, 2005, An overview of exploration and exploitation strategy for hydrocarbons in ONGC acreages of Jaisalmer Basin, Rajasthan: Proceedings of the National Seminar on Oil, Gas and Lignite Scenario with special reference to Rajasthan, April 20th, 2005, p. 53–68.</ref>) and possibly to those of the [[Kutch basin|Kutch]] and [[Saurasthra basin]]s to the west (see [[:file:M114CH03FG01.jpg|Figure 1]]). This deeper [[Mesozoic]] basin remains relatively poorly known and underexplored.

Structurally, the Barmer Basin is a typical intracontinental failed rift, bounded by normal extensional faults that display both north-northwest–south-southeast and north-northeast–south-southwest orientations (Figures 2 and 3). The basin is distinctly asymmetric in cross-section, with a regional dip to the east in the northern part of the basin, which flips to the west in the southern part. Fault-bounded horsts and ridges typically have a pronounced north–south elongation. Half-graben structures dominate, with deep synrift basins formed adjacent to footwall highs, the latter with evidence of crestal collapse and thinning of synrift stratigraphies onto the fault block highs indicative of significant initial rift topography. The presence of both hard- and soft linkages between faults is indicative of a long history of fault evolution in the basin. Older, isolated north-northwest fault segments are linked via younger north-northeast striking faults to form an extensive, through-going fault system. Individual faults connected as a result of fault-tip propagation, overstep, and subsequent breach of the intervening relay ramps (Bladon et al., 2014, 2015a, b). The resulting fault network provides fluid migration pathway linkages across long distances and vertically across thick shale sequences between otherwise isolated carrier beds and reservoirs.

[[file:M114CH03FG02.jpg|300px|thumb|{{figure number|2}} Depth-structure map constructed on top of the [[Fatehgarh Formation]] showing the main fields and important wells in the Barmer Basin together with the regional distribution of oil shows encountered in wells. See text for discussion of oil show classification and terminology (modified from Dolson et al., 2015<ref name=Dolsonetal2015 />). Geological cross sections of lines A–A’ and B–B’ are shown in [[:file:M114CH03FG03.jpg|Figure 3]].]]

The basin is shallowest in the north with pre and synrift sequences exposed at the surface, whereas the deeper, southern part of the basin has continued to undergo burial to the present day (Figure 3). The shallow northern end of the basin is underlain by a large basement high where large rift blocks form traps such as those at the Mangala, Aishwariya, and Bhagyam fields (Figure 2), and the main reservoir formations occur at depths of less than ∼ 1 km (∼0.6 mi) present day (Figure 3). North of these fields’ top seals are commonly absent in the basin with the main reservoirs being close to or exposed at the surface and have been so since the Miocene. The post-Miocene burial history of this northern part of the basin is constrained from vitrinite reflectance (VR) and apatite fission track analysis (AFTA) studies and is known to involve widespread differential uplift, tilting, and erosion. Although this uplift was centered on the northern part of the basin, amounts of uplift vary between individual fault blocks, creating complex fault block geometries that appear to increase in throw amount to the western side of the northern basin, where up to ∼1200 m (∼4000 ft) of erosion are recorded. Uplift and tilting has been a major driver of spillage and re-migration of hydrocarbons with vertical faults providing fluid migration routes. The basin deepens dramatically to the south, and a more complete post-Miocene succession is preserved, although broad inversion structures are still developed. The rapid deepening to the south coincides with a faulted basement hinge zone that controls the younger regional tilting in the basin and may represent a cross-rift transform fault system.

The basin is shallowest in the north with pre and synrift sequences exposed at the surface, whereas the deeper, southern part of the basin has continued to undergo burial to the present day (Figure 3). The shallow northern end of the basin is underlain by a large basement high where large rift blocks form traps such as those at the Mangala, Aishwariya, and Bhagyam fields (Figure 2), and the main reservoir formations occur at depths of less than ∼ 1 km (∼0.6 mi) present day (Figure 3). North of these fields’ top seals are commonly absent in the basin with the main reservoirs being close to or exposed at the surface and have been so since the Miocene. The post-Miocene burial history of this northern part of the basin is constrained from vitrinite reflectance (VR) and apatite fission track analysis (AFTA) studies and is known to involve widespread differential uplift, tilting, and erosion. Although this uplift was centered on the northern part of the basin, amounts of uplift vary between individual fault blocks, creating complex fault block geometries that appear to increase in throw amount to the western side of the northern basin, where up to ∼1200 m (∼4000 ft) of erosion are recorded. Uplift and tilting has been a major driver of spillage and re-migration of hydrocarbons with vertical faults providing fluid migration routes. The basin deepens dramatically to the south, and a more complete post-Miocene succession is preserved, although broad inversion structures are still developed. The rapid deepening to the south coincides with a faulted basement hinge zone that controls the younger regional tilting in the basin and may represent a cross-rift transform fault system.