Multi-stage hydrocarbon accumulation in Cambrian Xixiangchi Group, Pingqiao area, southeastern Sichuan and its implications for hydrocarbon exploration

doi:10.13745/j.esf.sf.2023.2.20

Abstract

Abstract:

The hydrocarbon accumulation in deep marine carbonate rocks generally involves multi-source, multi-stage processes, and an accurate analysis of such complex processes is necessary to help guide efficient oil and gas exploration. In order to determine the hydrocarbon accumulation processes in the Cambrian Xixiangchi Group, Pingqiao area, southeastern Sichuan, the multistage cementing materials within the reservoirs were investigated by cathodoluminescence microscopy, elemental and isotopic analysis, paleotemperature/pressure trapping in fluid inclusions, and bitumen analysis by laser Raman spectroscopy. The filling of cementing materials from early to late followed by the order of dolomite, calcite and quartz, with bitumen widely distributed in the dissolved pores of dolomite matrix and the filling dolomite grains. The cementing materials contained bitumen/gas inclusions in the dolomite layer and primary/secondary methane inclusions in the calcite layer. The diagenetic fluids were derived largely from host rocks, and calcite precipitation liked involved organic matter fluids. Based on the bitumen reflectance data (2.90%<BR_o<3.59%), combined with the homogenization temperature of the brine/bitumen two-phase inclusions and the hydrocarbon generation history of source rocks, it was inferred that bitumen was derived from pyrobitumen—a thermal cracking byproduct during liquid hydrocarbon charging from the Lower Cambrian Qiongzhusi Formation into the Cambrian Xixiangchi Group. The trapping pressure for the primary methane inclusions ranged between ~55.8-81.7 MPa (at trapping temperature of 198-203 ℃), indicating a pressure coefficient of 1.06-1.56 during thermal cracking in the burial period, consistent with moderate overpressure. The trapping pressure for the secondary methane inclusions ranged between ~42.1-65.0 MPa (at trapping temperature of 150-155 ℃), suggesting a pressure coefficient of 0.94-1.45 during shale gas charging from the Wufeng-Longmaxi Formations during the uplift period while still maintaining moderate overpressure. A multi-stage hydrocarbon accumulation model for the Cambrian Xixiangchi Group, Pingqiao area was established, which included liquid hydrocarbon charging in the Lower Cambrian Qiongzhusi Formation and in-situ cracking gas accumulation during the burial period, and shale gas charging in the Wufeng-Longmaxi Formations during the uplift period. This model provides a new direction and idea for hydrocarbon prospecting in the Cambrian Xixiangchi Group.

Key words: pressure evolution, diagenesis-accumulation dynamic evolution, multi-stage hydrocarbon accumulation, Xixiangchi Group, Pingqiao area, southeastern Sichuan

CLC Number:

TE121.1

GAO Jian, LI Huili, HE Zhiliang, CAI Xunyu, LI Shuangjian, LIU Guangxiang, YUAN Yusong, LIN Juanhua, LI Zhi. Multi-stage hydrocarbon accumulation in Cambrian Xixiangchi Group, Pingqiao area, southeastern Sichuan and its implications for hydrocarbon exploration[J]. Earth Science Frontiers, 2023, 30(6): 263-276.

Figures/Tables 11

Fig.1 Tectonic location and profile of well Pingqiao1 in southeastern Sichuan

Fig.2 Comprehensive stratigraphic histogram and tectonic evolution map in southeastern Sichuan

Fig.3 Microstructure and cathodoluminescence characteristics of minerals in the veins and pores from the Cambrian Xixiangchi Formation of well Pingqiao 1

Table 1 Carbon, oxygen, and strontium isotope data of the minerals and their host rock within the Cambrian Xixiangchi Formation of well Pingqiao 1

井名	层位	深度/m	岩性	δ¹³C_V-PDB/‰	δ¹⁸O_V-PDB/‰	⁸⁷Sr/⁸⁶Sr±2σ
平桥1井	洗象池群	3 135.09	白云石	-2.05	-11.13	N/A
		3 135.49	白云石	-2.29	-11.16	N/A
		3 135.21	白云石	-1.54	-11.03	0.709 643±0.000 011
		3 123.75	方解石	-15.59	-12.04	N/A
		3 026.56	方解石	-14.52	-11.19	0.709 237±0.000 009
		3 015.82	方解石	-8.38	-12.22	0.709 377±0.000 011
		3 135.21	泥晶白云岩	-2.70	-11.99	0.709 702±0.000 010
		3 026.56	泥晶白云岩	-0.73	-10.57	0.709 738±0.000 011
		3 015.82	泥晶白云岩	-1.32	-10.89	0.709 327±0.000 010

Fig.4 The distribution characteristic of carbon, oxygen and strontium isotope in dolomite, calcite and the proximal host rocks within the Cambrian Xixiangchi Formation of well Pingqiao 1

Fig.5 Chondrite-normalized rare earth element (REE) diagrams and δCe vs. δEu for dolomite, calcite and the proximal host rocks within the Cambrian Xixiangchi Formation of well Pingqiao 1

Fig.6 Raman spectra of bitumen (a) and reflectance results calculated by the Raman spectrum parameter of bitumen (b) in the Cambrian Xixiangchi Formation reservoir of well Pingqiao 1

Fig.7 Development characteristics of fluid inclusions trapped in the Cambrian Xixiangchi reservoirs of well Pingqiao 1

Fig.8 Laser Raman spectra (a, b), and trapping density-temperature-pressure (c, d) of fluid inclusion within the Cambrian Xixiangchi reservoirs of well Pingqiao 1

Fig.9 Modeling results of burial and thermal maturity histories of well Pingqiao1

Fig.10 Petroleum evolution model of the Cambrian Xixiangchi reservoirs of well Pingqiao 1

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