伊朗A油田白垩系Sarvak组隔夹层地质特征及成因

Geological characteristics and genesis of barriers and baffles of the Cretaceous Sarvak Formation in A Oilfield,Iran

基于岩心、薄片、地震、测井等资料,通过分析伊朗A油田白垩系Sarvak组生物碎屑灰岩储层内发育的隔夹层类型、地质特征及井震响应特征,系统研究了隔夹层的成因及展布特征。研究表明:A油田Sarvak组储层主要发育泥粒灰岩隔夹层和粒泥灰岩隔夹层,根据隔夹层发育的主控因素,可划分为沉积成因、成岩成因和复合成因。Sarvak组储层内隔夹层的展布特征具有明显的规律:厚度较大、广泛发育的隔夹层主要受沉积作用控制,沉积环境以局限台地相和潟湖相为主;厚度较薄、局部发育的隔夹层主要受压实作用和胶结作用等成岩作用控制。Sar2和Sar7段发育沉积成因隔夹层,平均厚度分别为15 m和5 m;Sar3和Sar8段局部发育成岩成因隔夹层,平均厚度分别为3.25 m和4.5 m左右;Sar4—Sar6段发育大量的复合成因隔夹层,厚度变化较大,总平均厚度为4.8~7.1 m,纵向上广泛发育。

The Iran A Oilfield of the Upper Cretaceous Sarvak Formation is a massive bottom-water bioclastic limestone reservoir with strong heterogeneity.Production preformation of oilfield indicated that barriers and baffles(BB)in the reservoir severely restricted the development of the oilfield.The type,porosity-permeability relationship,log response characteristics and identification criteria of BB in the carbonate rocks of the Cretaceous Sarvak Formation in the A Oilfield were analyzed through comprehensive study of cores,thin section and well logs,and the genesis and distribution characteristics of BB were systematically studied to evaluate the scale of BB developed in the oilfield.It is shown that two different types of BB mainly developed in Sarvak Formation,including wackestone BB and packstone BB,and according to the main controlling factors of BB development,they can be divided into sedimentary genesis,diagenetic genesis and sedimentary-diagenetic composite genesis which means that BB are affected by sedimentary environment in the early period and then porosity space further reduced by diagenesis later.The wackstone BB,with average thickness of 15m developed in Member 2 and with average thickness of 5m developed in Member 7 of Sarvak Formation,were controlled by the sedimentary facies including lagoon and restrict platform.The packstone BB,controlled by diagenetic genesis,is developed locally in Member 3 and Member 8 of Sarvak Formation with thickness about 3.25m to 4.5m.Penecontempo raneous cementation,burial compaction,burial cementation and dolomitization are the main diagenesis which caused the decrease of the porosity.In addition,a large number of thin BB is developed with variable thickness(about 4.8m to 7.1m)in Member 6-Member 4 of Sarvak Formation,which were controlled by both of sedimentary and diagenesis including compaction,cementation and dolomitization.It is concluded that the distribution of BB in Sarvak Formation have obvious rules in A Oilfield.The thick and stable BB developed in Member 2 of Sarvak Formation distribute in the whole research area,and the thin and local BB of Member 7 and Member 4 of Sarvak Formation is mainly developed in the west of research area.