Maximizing Production Efficiency: Geomechanical Assessment for Infill Well Optimization in Waterflood Developments in Crescent-Shaped Rim Structure Field, South of Oman

ABSTRACT: PDO's project portfolio includes numerous active waterflood developments, including a crescent-shaped rim structure field operating under Peripheral Waterflood with Flank Injection (PWRI). To enhance production rates, the proposed development plan involves infill drilling with reduced spacing between injectors and producers. However, this closer spacing could lead to potential risks associated with waterflood-induced fracturing, resulting in reduced sweep efficiency. In order to optimize the infill well spacing and minimize the risk of injector-producer short-circuiting and out-of-zone injection, a geomechanical assessment was conducted. Understanding formation fracture pressure and in-situ stress orientations was crucial for determining induced fracture directions relative to well azimuths. Given the crescent shape of the field and the outward orientation of most wells towards the flank direction, well azimuths varied from east to west. Injector wells were categorized into three groups based on the location: East, Crest, and West, with varying azimuth orientations. To determine stress orientation, borehole image (BHI) data from analog fields were analyzed to ascertain the expected orientation of maximum horizontal stress (SHmax). Detailed analyses using modified Hall's plot approach were conducted using injection pressure-rate data from 14 injectors to characterize current operating injection conditions (matrix vs. fractured). Field data from fracture pressure tests and analysis were interpreted to determine formation fracture pressure. Additionally, parameters such as injectivity, productivity, and depth of perforation relative to the Oil-Water Contact (OWC) were investigated to understand injection performance. Using these inputs, a calibrated PWRI frac model was developed to analyze fracture growth over time and pre dict fracture dimensions. The study revealed that producer wells in the East group were at higher risk of potential water breakthrough from induced fractures from injectors, as they were along the intersection path of propagating fracture directions. Modeling results showed that un der an injection rate of 2000 m3/day over 25 years, the maximum predicted fracture (half) length reached approximately 350 m (i.e., the field's end of life). Producer wells in the West group had a lower risk due to their well directions being approximately parallel to the direction of fracture propagation, while wells in the crest area were assessed to have a medium risk. These findings demonstrated that using a constant spacing for the entire field was not an optimal solution. Minimizing the risk of early water breakthrough and short-circuiting was essential in determining spacing. The study's results provided valuable guidance on operational injection pressures for waterflood optimization and improved recovery efficiency.