Automated Rate Control to Prevent Induced Fracturing and Fracture Opening Monitored with Step Rate Tests

Abstract

Abstract Designed and occasionally induced fracturing occur during injection and production operations in petroleum, geothermal energy, and geological CO2 storage. Although the goals and perspectives vary across industries, fracture monitoring and control remains crucial. Induced fracturing enhances petroleum and geothermal energy production, whereas its prevention is a key challenge in CO2 storage. Therefore, incorporating fracture management into automated injection control would be beneficial as enabled by the recent wide deployment of permanent well surveillance technologies. This paper presents a new automated injection control approach based on on-the-fly interpretation of step-rate tests (SRT) commonly used in induced fracture monitoring. The paper explores single-phase isothermal water injection, which is relevant for describing water injection in hydrocarbon reservoirs (after forming the invaded area around the wells) and in saline aquifers. The injection control approach employs time-lapse pressure transient analysis (PTA-SRT) for SRT interpretation and constructing safe operating envelopes (SOE) representing the no-fracture response based on pressure derivative curves. When deviations from the SOE happen, the controller automatically reduces the injection rate to limit fracture growth, and continuously monitors the pressure response for the updated rate. The paper demonstrates the results of testing of the injection control approach with step-rate test data from synthetic well simulations and a real case for water injection in an oil-bearing formation on the Norwegian Continental Shelf. The simulations use a proxy model for pressure-dependent fracture permeability matched against field measurements. The testing results confirmed the effectiveness of the control approach in detecting induced fractures shortly after their onset and preventing further fracture growth by applying immediate rate adjustments. Through successive rate changes and monitoring of the pressure response, the controller can optimize the injection rate while keeping the well pressure within the safe operating envelope. The automated injection control workflow differs from existing industry practices through the integration of PTA with the safe operating envelope concept. Fracture detection with the PTA-SRT approach only requires one rate step after fracture opening, whereas standard industry workflows such as p-Q curve analysis typically requires 2-3 rate steps. In addition, the PTA-SRT approach is resistant to noise, step duration and rate stepping, making it appealing to real field SRT applications.