Learning from Water Injection Pilot in a Low Permeability Reservoir Developed with Hydraulically Fractured Horizontal Wells – ABH Field Case Study

Abstract

Aishwariya Barmer Hill (ABH) is a Porcellanite oil reservoir located in the northern part of Barmer Basin in India. The formation has low permeability of ~1mD, an average porosity of 25% and has in-situ oil viscosity of ~3 cP. The ABH field has been developed with long horizontal wells with multistage hydraulic fracturing under depletion drive. The current estimated RF is 10-12% on depletion drive. To improve the RF, water flood was evaluated as the next stage of development. This paper discusses the results of water injection pilot within a complex setting with hydraulically fractured producer (observation) wells and impact of injection below and above frac pressure. Two short term injectivity tests and one long term injection pilot have been conducted in ABH field. Concepts like injection above and below frac pressure and injection in a hydraulic fractured well and a non-hydraulic fractured well were tested. The long-term injection pilot comprised of a vertical injector and two hydraulically fractured horizontal producers on it's either side. As the injection pressure was above frac pressure, data like time lapse Pressure Fall Offs (PFOs) was acquired to understand waterflood induced frac parameters. Production logging and bottom-hole pressure surveys were also conducted to understand injection profiles. Minimal injectivity was attained below frac pressure but good injectivity with sustained rate was observed above it. PTA analysis shows that fractures are induced due to water injection and time lapsed PFOs were analyzed to estimate the induced fracture parameters. Some unique signature of frac closure was also observed in PTA. Increase in water cut of one of the producer well was observed, however most of the injected water was getting imbibed into the reservoir. Role of injection water quality was also evaluated which may cause drop in injectivity and continuous frac growth. Numerical simulation was carried out to history match the observed injection performance. This indicated changes in effective permeability during injection and shut-in periods. Careful consideration of injection pressure, well design and pattern selection is critical for designing water flood in a low permeability reservoir with hydraulically fractured wells and this pilot was able to answer many questions related to it. The pilot suggested that below frac pressure injection may be required in on-trend well pattern. Poor quality injection water can cause growth of induced fracture. Response time on producer is a key consideration impacting project economics. Improving recovery from tight field development is a key area of focus and ABH pilot results will help to understand /solve some of the key considerations related to it.