渝东南地区深部煤层气成藏特征及有利区评价

Reservoir forming characteristics and favorable area evaluation of deep coalbed methane in southeastern Chongqing

渝东南地区南川区块二叠系龙潭组煤层气井Y2井直井自喷日产气1.3×10^(4)m^(3),展现了深部煤层气良好的勘探潜力,但深部煤层气的成藏特征尚不明确。以南川—新场—丁山区块为研究对象,基于煤层气井试井资料、测试化验资料及试采分析,开展了深部煤层气成藏特征及“甜点”区研究。结果表明:研究区龙潭组深部煤层气受沉积差异控制,南川区块发育潮坪—碳酸盐岩台地沉积,煤层2~4层,总厚度2~8 m,往丁山区块为潮坪沉积,发育煤层6~8层,总厚度5~10 m;深部煤储层中高演化,R_(o)为1.7%~2.4%,微孔和微裂隙发育,吸附气存于微孔中,游离气主要储集于微裂隙中,储层具备吸附气与游离气共同赋存的条件;顶底板以灰岩和泥岩为主,封盖能力强,地层水矿化度大于10 g/L,水型为CaCl_(2)型,保存条件好;深部煤层气具有“中高演化、高含气、保存有利区富含游离气以及微裂隙储集”的富集规律。建立了深部煤层气地质工程“双甜点”评价指标16项,划分了3类“甜点”区,优选1500 m以深有利区面积2599 km^(2),估算资源量5457×10^(8)m^(3)。研究成果对南方深部煤层气的勘探具有指导意义。

The coalbed methane Y2 well of the Permian Longtan Formation in Nanchuan Block of southeastern Chongqing has a daily gas production of 1.3×10^(4)m^(3),demonstrating good exploration potential for deep coalbed methane.However,the reservoir characteristics of deep coalbed methane are not yet clear.Taking Nanchuan-Xinchang-Dingshan block as the research objects,the reservoir characteristics and sweet spot areas of deep coalbed methane was researched based on the data analysis of coalbed methane well test,testing and production test.The results showed that the deep coalbed methane in Longtan Formation in the study area is controlled by sedimentary differences.Nanchuan Block develops tidal flat carbonate platform deposits,with 2~4 coal seams and a total thickness of 2~4 m.Dingshan Block is tidal flat deposits,with 6~8 coal seams and a total thickness of 5~10 m.Deep coal reservoirs have high evolution,with R o ranging from 1.7%to 2.4%.Pores and fractures are developed,and adsorbed gas is stored in micropores.Free gas is mainly stored in macropores and cleavage fractures.The reservoir has the conditions for the co occurrence of adsorbed gas and free gas.The top and bottom plates are mainly composed of limestone and mudstone,with strong sealing ability.The mineralization degree of the formation water is greater than 10 g/L,and the water type is CaCl_(2),with good preservation conditions.Deep coalbed methane has the characteristics of medium to high evolution,high gas content,high saturation,and abundant free gas in favorable preservation areas.We have established 16 evaluation indicators for deep coalbed methane geological engineering double sweet spots,divided them into 3 types of sweet spot areas,and selected a favorable area of 2599 km^(2)with a depth of 1500 m.The estimated resource amount is 5457×10^(8)m^(3),which has guiding significance for the exploration of deep coalbed methane in the south.