Real-Time Microseismic Mapping Helps Understanding Hydraulic Fracture Geometry, Drainage Patterns, and Oilfield Development Optimization: A Case Study in the Changqing Field
Authors: Lu Hongjun , Wang Chengwang , Yin Qi , Bai Xiaohu , Zheng Guangjie , Traweek Ryan , Salahudin Sharifudin , Lin Wei 
Published: March 2015

Abstract
The Changqing field is one of the largest fields in China, yet it is characterized by low permeability, low initial pressure, and low reservoir quality. During the past few years, technological advancements within the oil industry, horizontal drilling, and hydraulic fracture stimulation have helped create a development boom in this field, with total production of barrel of oil equivalence (BOE) reaching 50 million tons in 2013.
Located in the Ordos basin of China, the primary pay formation of the Changqing field is Triassic, which features a complicated sedimentary system. 72.8% of reservoirs in the Changqing field have permeability lower than 1.0 md. Although it was apparent that all of these wells would require fracture treatments to help achieve optimum production, it was difficult to identify a routine treatment design or fracturing strategy to extend to all of the reservoirs because the Changqing field has 19 oilfields and three gas fields stretching over five provinces. The sediment source of the pay formation varies in terms of direction and lithology, and all of the sedimentary systems vary from fan delta to braided stream delta systems.
To maximize well production, it is necessary to analyze the differences among these fields and identify the most favorable fracture treatment design for each field. Microseismic mapping has proven to be a valuable technology for assessing and optimizing the fracture treatment by describing fracture geometry. This paper introduces a real-time microseismic mapping project conducted on a multistage fracture treatment in a specific tight sand reservoir of Changqing; during this project, a quantifying relationship between the fracture treatment parameters and stimulated reservoir volume (SRV) was realized, enabling stimulation optimization in this area. This paper details the microseismic mapping acquisition, hydraulic fracture symmetry, practical drainage pattern, evaluation of the fracture treatment parameters, and perforation strategy that impact fracture geometry and SRV as well as optimization in this particular tight sand reservoir.

Introduction
Located in northern middle China, the Ordos basin (Fig. 1) is the second largest depositional basin, covering an aerial extent of approximately 370,000 square kilometers, stretching across the Shaanxi, Gansu, Shanxi, Ningxia, and Inner Mongolia, with original oil in place (OOIP) of approximately 8.6 billion tons. The Ordos basin is a superimposed basin having experienced multiple tectonic movements. The stratigraphic fill of the Ordos basin is composed of numerous facies. These types vary between Carbonate Platform, Clastic sedimentary of Paleozoic, fluvial, delta, and lacustrine of Mesozoic; its total thickness is approximately 5000m. In the Ordos basin, hydrocarbon contribution formations of Triassic and Jurassic produce oil; whereas, Permo-Carboniferous and Ordovician produce gas. Across the entire board of the basin, oil reservoirs are distributed in the southern portion, while gas reservoirs are abundant in the northern part. Because of complex tectonics characteristics and low permeability, reaching its current total production of BOE of 50 million tons per year proved overwhelmingly difficult. Before the 1950s, it took 50 years to achieve production of 2,000 tons per year; it then took another 20 years to achieve production reaching 20,000 tons. Even up to the year 2000, production was only 7.5 million tons per year. In the last 10 years, as conventional sources of oil and gas have declined, operators have been driven to explore unconventional resources globally, and the Changqing field had made astonishing progress during this period.