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.

Luohe ultra-low permeability sandstone reservoir is a hot block in Yanchang oilfield, which is a potential point for increasing production and reservoir. In view of the current situation that there is no unified stress sensitivity evaluation standard for ultra-low permeability sandstone in the study area, taking the ultra-low permeability sandstone in Luohe district as the research object, the stress sensitivity evaluation of ultra-low permeability sandstone is carried out by using experimental analysis as the main means. The results show that it is more accurate to evaluate porosity by using pore stress sensitivity coefficient instead of pore compressibility coefficient. With the increase of net overburden pressure, the porosity stress sensitivity decreases gradually; the permeability stress sensitivity is evaluated by variable confining pressure. With the increase of confining pressure, the permeability damage decreases. With the decrease of confining pressure, the permeability damage increases, but it can not recover to the original value, so the permeability damage is irreversible; in the low bottom hole pressure stage, stress sensitivity has a greater impact on oil well productivity, while in the high bottom hole pressure stage, stress sensitivity has a smaller impact on oil well productivity; advanced water injection can reduce the adverse effect of stress sensitivity on the development of ultra-low permeability sandstone and maximize the economic benefits. The research results clarify the method of stress sensitivity evaluation, and provide guidance for efficient water injection in the next step.