Research On Tight Sandstone Reservoir Distribution And Geological Adaptability Of Horizontal Well Of The8^Th Member Of Shihezi Formation And The1^St Member Of Shanxi Formation In Eastern Sulige Gasfield, Ordos Basin

Abstract:The paper mainly studied on sedimentary facies types and its’distribution, reservoir characteristics and its’distribution, comprehensive evaluation, and analyzed furtherly on geological adaptability of horizontal well deeply of the8th member of Shihezi formation and the1st member of Shanxi formation in eastern Sulige Gasfield, Ordos basin. Channel-fill deposit and mid channel bar deposit in braided river system, channel-fill deposit and point bar in meandering river are considered as favorable sedimentary microfacies in the study area. The sandbody is controlled by depositional system. The sedimentary facies spatial distribution shows extending from the north to the south. According to architectural firtures of the sandbodies, braided river system can be divided into three facies of superimposed belt, transition belt and depression belt. Superimposed belt is of thick sandbodies and can be the main target for drilling horizontal well, The river experienced a strong migration and sands distributed widely in the transverse multi-channel, and resuted in superimposed sandbodies vertically, due to a strong hydrodynamic condition during the lower part of the8th member of Shihezi formation. However, hydrodynamic condition was weak and the river is narrow during the upper part of the8th member of Shihezi formation and the1st member of Shanxi formation, led to undeveloped sandstones distributed mainly on the transition and depression belt. Analysis of reservoir petrology characteristics shows that the8th member of Shihezi formation and the1st member of Shanxi formation sandstone reservoirs are mainly composed of litharenite and sublitharenite. Kaolinite, hydromica, siliceous materials, iron calcite are the major interstitial materials in the sandstone reservoir, and with small amount of chlorite, siderite, tuffaceous material and ankerite. Reservoir pore types mostly are secondary dissolution pores. Pore structure analysis indicates that the8th member of Shihezi formation and the1st member of Shanxi formation sandstone reservoir has intense heterogeneity with uneven pore and throat sorting and poor connectivity.We divided geological model5types of horizontal wells:thick massive solitary sandbody, sandstone vertically stacked type with tight interlayers, sandstone vertically stacked type with argelliceous interlayers, horizontal cutting sandstone connected types and lateral sandstone tomatoes-on-stick types, based upon analysis of horizontal well geological features, anatomizing sandstone architecture of high density well-patterns. Among these modles the thick massive solitary sandbidy, sandstone vertically stacked type with tight interlayers are the most important types for horizontal wells. Basis on the different stage, horizontal wells’ target area can be devided into two types: horizontal well entirety development area and high density horizontal well-pattern development. The southern area of the study area is suitable for the high density horizontal well-pattern development, whereas the northern part can adopt the former due to its still in low developement stage.This research result is important in practical guidance in tight reservoir evaluation, prospective gas-bearing area prediction, regulation and deployment of technical proposals for horizontal well development and evaluating on adaptability of horizontal wells.