Understanding Tight Oil Reservoir Hydraulic Fracturing Stimulation Using Two Wells Simultaneous Micro Seismic Monitoring Approach

Abstract

The tight sand oil reservoir found in the Ordos basin is known for its very low porosity and permeability. Almost every well has been stimulated using hydraulic fracturing techniques. The average production for a vertical well is approximately 4–5 tons per day. Among such a large number of fracture jobs, enhanced production after stimulation does not always meet expectations. Since2005, hydraulic fracturing monitoring services have been carried out widely in this field to improve fracture geometry understanding and optimize well placement. With the implementation on-site, real-time hydraulic fracture monitoring, the pumping procedure can be adjusted accordingly based on the mapped microseismic events. Based on the past hydraulic fracturing monitoring experience in this field, an average microseismic event detectable distance range around 300 m is expected for the case of geophones inside a monitor well. Two parallel horizontal wells were thus drilled at 600m apart. Horizontal section length is around 1,500m for both wells. The original hydraulic fracture plans for each well consisted of 18 stage stimulations, but were subsequently adjusted to 13stages based on real-time hydraulic fracture monitoring results. Three monitoring wells were drilled from toe to heel as shown in Figure 1. These monitor wells will also be used as water injection wells in later secondary recovery processes. So hydraulic fractures generated by the pumping from both horizontal wells are not expected to extend far enough to reach the monitor wells. With this favorable well layout, simultaneous dual-well hydraulic fracture monitoring was proposed and conducted. In order to obtain the optimized fracturing parameters first, the initial 3 stages of each treatment well was conducted at one stage per well i.e. stimulate well-1 and then move to fracwell-2. Simultaneous hydraulic fracturing began after the initial six stages were completed.

An Overview of New Developments in Shale Gas: Induced Seismicity Aspect

“…They argued that by correlating the results of the two techniques in parallel could provide valuable information about the local heterogeneity within the reservoir and the effect on the fracture simulation programs. Xu et al [45] presented results of microseismic monitoring of hydraulic fracturing simulation in a tight sand reservoir. They stated that although the use of a single well has been widely adopted, much better results could be obtained with a dual-well set up regarding fracture delineation and location accuracy.…”

“…Xu et al [45] studied the hydraulic fracturing stimulation using microseismic monitoring of two wells simultaneously in low porosity and low permeability formation in Ordos basin with the aim of improving fracture geometry and optimization of good placement. Comparing with single-well microseismic monitoring, they concluded that the dual-well technique could explain features in far more precise details and accuracy and then subsequently can reduce uncertainty.…”

Experimental Research of Compound Monitoring on Multiple Temporary Blocking Refracturing for Long-Section Horizontal Wells

“…As the basic principle of the monitoring process is through acoustic emission and seismology (Wang, 2008;1 ), microseismic events do not necessarily occur where the fracturing fluid arrives or where the fracture expands (Liu, 2012;2 ). But, it can be attributed to the characteristics of induced microseismic signals, such as different energy, weak signal, wide frequency band, and serious interference by background noise and low signal-to-noise ratio (SNR) which affects the accuracy, reliability, and subsequent interpretation of microseismic research (Kurdi et al, 2015).In comparison, the main mechanism of hydraulic fracture is tensile failure, while that of microseismic events with high amplitude is usually associated with shear failure (Xu et al, 2013).…”

“…Hence, one monitoring method may not be able to fully analyze and represent the reservoir properties. Hence, for a better understanding and analysis, the combination of variety of monitoring methods (Liu et al, 2014;Hickey et al, 2019;Young et al, 2020) is preferred.…”