An Integrated Disciplinary Approach Towards Hydraulic Fracturing Optimization of Tight Oil Wells in the Ordos Basin, China

Abstract

Exploiting the vast quantities of in-place oil in some of China's large sedimentary basins will require understanding and identifying where new technologies and techniques can be applied to maximize production. Exploration in the Ordos basin in north-central China has demonstrated that tight oil reservoirs, such as the Chang 7 formation, are widely distributed; however, they remain relatively underdeveloped. These reservoirs are buried below the conventional oil layers, differ from them by geological composition, and their thin pay zones and low permeability present development challenges.As part of a standard exploration and appraisal program, multiple vertical wells have been drilled to characterize the Chang 7 reservoir quality, and many were completed with only one hydraulic fracturing stage. Unfortunately, average hydrocarbon production was often low, and horizontal well completions with multiple transverse hydraulic fracturing treatments were required to obtain commercial flow rates. Part of the integrated workflow developed for the stimulation program requires the capture of reservoir, geological, and geomechanical properties for use in the design of the stages. The perforations were designed to allow for effective fracturing treatments across the lateral and were placed using the abrasive perforating technique. Additionally, one of these vertical wells was used for real-time microseismic fracturing monitoring to evaluate fracture geometry, fracture orientation, and azimuth.Real-time technology and an integrated workflow effectively increased the understanding of where, when, and how to deploy hydraulic fracturing treatments in the lateral section of the study well. This optimization has resulted in more than an 8-fold increase in production compared to that from vertical wells. Considered a breakthrough, this project has resulted in the planning for additional horizontal wells. Geology OverviewThe Ordos basin is the second largest onshore oil-and gas-producing basin in China, covering an area of 370,000 km 2 and including parts of the Shaanxi, Shanxi, and Gansu provinces and Ningxia Hui and Inner Mongolia autonomous regions. The basin is a large-scale asymmetric syncline, considered to be a stable Craton basin, and is bounded by the Huanghe fault in the north, Jinhuashan-Qishan Mountains in the south, the Zhouzishan-Luoshan Mountains to the west, and the Luliang Mountains to the east.The Yanchang formation (Fig. 1), deposited during the Triassic period, has a wide presence across the Ordos basin. It consists of the Chang 6, Chang 7, and Chang 8 reservoir sandstones, which are stacked sand and shale deposits. These layers are a result of comprehensive series of continental river, delta, and lake depositional systems; the Yanchang Group of the Upper Triassic is the primary oil-producing layer. These layers are typically low porosity and low permeability and can be characterized as a fine grain size with microthroats and poor physical properties. The formation is mainly composed of 38.9% quartz, 20.8% feldsp...

Hydraulic Fracturing Shear/Tensile/Compressive Crack Investigation Using Microseismic Data

“…Moreover, for all the GD results, their nodal lines are very close, approximately along the northeast-southwest (NE-SW) direction, which indicates that the GD model based focal mechanism inversion can help in characterizing the fracture geometry. According to the contractor, the minimum horizontal principal stress in the study region is approximately along the northwest-southeast (NW-SE) direction [41]. The inversion results agree with the rock mechanics study on that the fracture plane is generally perpendicular to the direction of the minimum principal stress [42].…”