松辽盆地杏树岗油田低渗透储层裂缝发育特征

Fracture development characteristics of the low permeability reservoirs in Xingshugang oilfield of Songliao Basin

杏树岗油田储层为低孔—低渗(特低渗)储层,裂缝对该区储层的油气富集及产能具有重要影响。该区主要发育构造缝和成岩缝,其中构造成因的剪切缝和张性缝最为发育,是该区的主要裂缝类型。构造缝以大于75°的高角度缝和直立缝为主,充填程度差,有效性好。裂缝发育方位为NE、NW及近SN,其中NE向裂缝在该区占优势。明水组沉积末期是该区裂缝的主要形成时期,主要形成NE向高角度(直立)张性缝缝。裂缝的发育分布与岩性、层厚、构造位置等因素有关;岩性不同,裂缝发育程度也不同;随着层厚的增大,裂缝间距变大,密度减小,裂缝发育程度显著降低;裂缝与构造部位(断层)关系密切,随着距离断层越来越远,裂缝密度呈递减趋势,发育程度也明显降低;裂缝发育好的地区位于工区中部较大规模断裂带两侧以及多组断裂带交汇地带。研究成果对该类油藏的有效开发具有重要的借鉴作用。

Reservoirs in the Xingshugang oilfield are low porosity-low permeability(extra low permeability).Fractures had made important contributions to hydrocarbon accumulation and productivity in the oilfield.Structural fractures and diagenetic fractures are common,with the dominance of tectogenetic shear fractures and tension fractures.Structural fractures are dominated by high angle fractures of over 75° and vertical fractures,which are poorly filled and effective.The fracture orientation involves NE,NW and near SN,with NE fractures being the dominant.The late Mingshui formation was the major period when fractures were formed,with NE high angle(vertical) tension fractures being the dominant.The distribution of fractures was related to factors such as lithology,formation thickness and structural location;the development of fractures is different in different lithologies;with the increase of formation thickness,fracture spacing enlarges,fracture density reduces,showing significant reduction in the degree of fracture development;fractures are closely related with tectonic position(faults);with the distance to fault increases,fracture density presents a decline trend and the degree of fractures development also sharply reduces.Fractures were well developed on both sides of the large-scale fault zone in the middle of the study area and in the intersection zone of multiple faults.The result of this study is significant to efficient development of similar reservoirs.