川东北地区长兴组酸性气藏中硫化氢来源及成因

doi:10.11743/ogg20150202

摘要/Abstract

摘要： 川东北地区长兴组（P₃ch）和飞仙关组（T₁f）天然气藏中检测出的高浓度H₂S气体目前被认为是硫酸盐热化学还原作用（TSR）成因。然而，长兴组内并无类似于飞仙关组的膏岩层或硬石膏结核发育，因此长兴组气藏的酸化过程成疑。通过针对研究区地层古压力以及输导体系方面的探讨，并结合碳酸盐岩晶格硫酸盐（CAS）含量、同位素以及稀土微量元素分析，研究认为:①长兴组气藏中高浓度H₂S气体不太可能由飞仙关组酸性气藏“倒灌”形成，而是由本地地层中发生的TSR作用所导致；②嘉陵江组（T₁j）和黄龙组（C₂h）沉积时期蒸发性卤水以及长兴期海水并非主要来源，而飞仙关期蒸发性卤水的倒灌为长兴组TSR反应的发生提供了主要的SO₄^2-来源，并导致其内的TSR成因方解石具有与飞仙关组方解石相似的正Eu异常、高Sr（高达7 767×10^-6）和Ba含量（高达1 279×10^-6）以及相对同时期海水较高的⁸⁷Sr/⁸⁶Sr比值（0.707 24～0.707 55）；③卤水穿层流动主要发生于沉积期或成岩早期，沉积-准同生期渗透回流作用和早-中埋藏阶段差异压实作用为卤水运移的主要机制；④长兴组白云岩化过程中释放的CAS也可能是重要的SO₄^2-来源，并导致该层位气藏中H₂S及储层沥青δ³⁴S值较飞仙关组略有偏负。

关键词: 晶格硫酸盐, 差异压实, 硫酸盐热化学还原反应, 硫化氢, 酸性气藏, 长兴组, 川东北地区

Abstract: High H₂S concentrations found in gas reservoirs within the Upper Permian Changxing Fm(P₃ch)and Lower Triassic Feixianguan Fm(T₁f)are generally thought to be formed via a process known as thermochemical sulfate reduction(TSR).However,unlike the T₁f Fm,rare gypsum/anhydrite beds or anhydrite nodular were found in the P₃ch Fm.This cast doubts over the accepted model for the souring process of the P₃ch reservoirs.This study provides an analysis of palaegeopressure and carrier system within this system using carbonate-associated sulfate(CAS),isotopes,trace and rare earth element data.Results shows that,the H₂S of high concentrations within the P₃ch reservoirs were not derived from downward migration of sour gas from the T₁f Fm,but were generated in situ through TSR;reactive sulfates were mainly derived from cross-formational brines migration from the T₁f Fm,but with insignificant contributions from the Late Permian P₃ch seawater and sulfate-rich brines within the Lower Triassic Jialingjiang Fm and Middle Carboniferous Honglong Fm formations,and the down-migration of T₁f brines may have resulted in the P₃ch TSR calcites having positive Eu anomaly,high Sr contents(up to 7 767 ppm)and Ba contents(up to 1 279 ppm)close to the T₁f TSR calcite,and ⁸⁷Sr/⁸⁶Sr ratios(0.707 24~0.707 55)more radiogenic than those of the late Permian seawater;the cross-formational brine flow mainly occurred during sedimentary stage or the early stages of diagenesis,and seepage reflux during contemporaneous-penecontemporaneous stage and differential compaction flux during early-mid burial stage might serve as the main migration mechanisms;④CAS released during dolomization was another possible sulfate source,which brought the δ³⁴S values of H₂S and bitumen a little lower than those of the T₁f Fm.

Key words: CAS, differential compaction, TSR, H₂S, sour gas reservoir, Changxing Formation, northeastern Sichuan Basin

中图分类号:

TE122.1

李开开,蔡春芳,姜磊,等. 川东北地区长兴组酸性气藏中硫化氢来源及成因[J]. 石油与天然气地质, 2015, 36(2): 183-192. doi: 10.11743/ogg20150202 Li Kaikai,Cai Chunfang,Jiang Lei,et al. Origin of H₂S in sour gas reservoirs in the Upper Permian Changxing Formation in northeastern Sichuan Basin[J]. Oil & Gas Geology, 2015, 36(2): 183-192. doi: 10.11743/ogg20150202

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