鄂尔多斯盆地苏里格气田辫状河体系带特征

Characteristics of braided river sedimentary system zones in Sulige gasfield,Ordos Basin

鄂尔多斯盆地苏里格气田上古生界气藏石盒子组8段、山西组1段主体为河流相沉积,河道多期切割、叠置,形成了规模较大的"辫状河体系"。根据沉积条件和沉积特征的差异,可分为叠置带、过渡带和体系间3个辫状河体系带。研究深化并发展了辫状河体系带的概念及沉积内涵,建立了沉积相-辫状河体系-辫状河体系带的多级沉积格架,提出了辫状河体系带的多参数定量划分标准。综合分析岩心、测井、钻井等资料,认识到辫状河体系带对沉积微相展布和规模、砂体的叠置样式、有效砂体的类型和集中程度具有较强的控制作用,是控制气田沉积、储层的关键地质因素。叠置带心滩发育频率高,规模大,砂体多期叠置,有效砂体富集,是气田开发的主力相带单元,过渡带河道充填发育,有效砂体以孤立型分布为主,辫状河体系间砂体零星发育,开发潜力较差。分别针对叠置带、过渡带建立了水平井地质目标优选标准,优化了井轨迹,为水平井随钻地质导向提供了更可靠的地质依据。

The 8thMember of the Shihezi Formation and the 1stMember of the Shanxi Formation of the Upper Paleozoic in Sulige gasfield are mainly of fluvial facies,and the crosscutting and superimposition of multiple-stage channels resulted in a large ＂braided river system＂in geologic history. According to different sedimentary environments and sedimentation characteristics,the braided river system can be divided into superimposed zone,transitional zone and inter-channel zone. This study deepens and develops the concept and deposit connotation of the braided river system,establishes a sedimentary hierarchy of sedimentary facies-braided river system-braided river system zone,and proposes multiple-parameter quantitative classification standards for Sulige＇s braided river system. Through integrated analysis of core,logging and drilling data,it is concluded that braided river system zone is the key geological factor for sedimentation and reservoir characteristics of Sulige gasfield,as it strongly controls the sedimentary microfacies distribution and scale,sand bodies＇ superimposition style and effective sand bodies＇ type and centralization. The superimposed zones of the braided river system feature in highly developed and large channel bars,superimposition of multiple stage sand bodies and clustering of effective sand bodies,thus is the favorable facies zone for gas production. In transitional zone,channel filling is more developed and effective sand bodies are mainly distributed in isolation in space. In contrast,the inter-channel zone is characterized by scattered and sparse sand bodies,thus its exploitation potential is poor. In addition,the criteria of geological target selection for horizontal wells are set up for the superimposed zone and transitional zone of braided river system respectively,and horizontal well trajectory is optimized,providing a more reliable basis for geo-steering while drilling of horizontal wells.