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==Introduction==

==Introduction==

The Barmer Basin of northwestern Rajasthan, India (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; Compton, 2009; Dolson et al., 2015). Sediment thickness exceeds 6 km (4 mi) in the main depocenters, 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 immediately to the south (Biswas, 1987; Banerjee and Rao, 1993; Banerjee et al., 2002; Figure 1). Significant exploration potential remains in deeper structural plays and in post-rift stratigraphic traps (Kothari et al., 2015).

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>).

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 margin of the basin. A summary of the current understanding of the petroleum geology of the basin is given in Dolson et al. (2015), while Farrimond et al. (2015) detail the aspects of the main source rocks and their properties. This chapter 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 and gas fields in the Barmer Basin, the evolution of migration pathways, 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 (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.

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.

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.