辫状河致密砂岩气藏阻流带构型研究——以苏里格气田中二叠统盒8段致密砂岩气藏为例

传统的阻流带构型研究通过分析剩余油与隔夹层的空间组合关系来指导剩余油的挖潜,而对于流动性明显好于油藏的气藏中阻流带构型的研究则较少。为此,以鄂尔多斯盆地苏里格气田辫状河流相储层为例,在储层构型层次分析理论的指导下,以野外露头剖面和大量实钻水平井解剖为基础,结合生产动态分析和气藏工程验证,研究致密气阻流带存在的依据、构型级次、成因类型及规模参数,建立阻流带构型模型,并进行验证。结果表明:(1)苏里格气田辫状河复合有效砂体内存在泥岩或细粒沉积阻流带,并且阻流带是导致直井与水平井动态特征差异、直井泄气半径与实测有效砂体长度不吻合的主要原因;(2)大型辫状河阻流带可划分为河道复合体间(一级)、心滩单砂体间(二级)、心滩单砂体内(三级)共3个构型级次,其中二级阻流带包含河道间泥、泛滥平原泥、致密砂3种成因类型,三级阻流带包含落淤层及坝上沟道2种成因类型;(3)阻流带的几何形态、规模尺度、视厚度等参数差异较大,该气田中二叠统下石盒子组8段气藏水平井平均1 000 m水平段可钻遇各类型阻流带5~7个,单个视厚度介于10~200m;(4)阻流带叠置样式可划分为孤立型、侧向叠置型、堆积垂叠型和切割垂叠型等4种构型模型;(5)较之于直井,运用该研究成果,在苏里格气田通过水平井钻穿阻流带可提高天然气储量动用程度13.02%,并建议1 000 m水平段合理压裂段数介于6~8段。

An architectural study on the blocking zone of braided river tight sandstone reservoirs: A case study on the tight sandstone gas reservoirs of the 8th Member,Shihezi Fm,Middle Permian in the Sulige Gas Field,Ordos Basin

Traditional architectural studies on blocking zones could be usually found on analyzing the spatial relationship between remaining oil and intercalations to guide the potential tapping of remaining oil, while few literatures could be searched for focusing on the architecture of blocking zones in the gas reservoirs the fluidity of which is much better than that of oil reservoirs. In this paper, the braided river reservoirs in the Sulige Gas Field, Ordos Basin, were taken as examples. Under the guidance of reservoir architectural hierarchical analysis theory, based on field outcrop section and abundant analysis of actual horizontal wells, combined with production performance analysis and gas reservoir engineering verification, the existing evidence, grade classification, genetic type and scale parameters of blocking zones were studied, and its architecture model was established and verified. And the following research results were obtained. First, there is a blocking zone of muddy or fine-grained sediment in the effective composite sandbody of braided river in the Sulige Gas Field, and it is the main factor leading to the production performance difference between vertical well and horizontal well and the mismatch between the gas drainage radius of vertical well and the measured length of effective sandbody. Second, blocking zones of large scale braided rivers can be divided into three architectural grades: Grade I (between composite channel sandbody), Grade II (between channel bar single sandbody) and Grade III (inside channel bar single sandbody). Grade II blocking zone includes three genetic types, i.e., inter-channel mudstone, floodplain mudstone and tight sandstone, and Grade III blocking zone includes two genetic types, i.e., silt layer and channel on bar. Third, the parameter values of different blocking zones are more different, such as geometry, scale and apparent thickness. On average, 5–7 diverse blocking zones can be drilled in 1 000 m horizontal section of horizontal wells in the gas reservoir of the 8th Member of Lower Shihezi Fm of Middle Permian in the Sulige Gas Field, and the apparent thickness of each blocking zone is 10–200 m. Fourth, the blocking zone superposition patterns can be divided into 4 architectural models, i.e., isolated model, lateral superposition model, vertical stacking superposition model and vertical cutting superposition model. Fifth, compared with vertical well development, horizontal well development can improve the producing degree of natural gas reserves in the Sulige Gas Field by 13.02% through penetrating the blocking zones. It is recommended to carry out 6–8 fracturing stages in 1 000 m horizontal section.