Abstract
Petroleum Development Oman (PDO) has recently embarked on a journey towards maximizing reservoir throughput and improving waterflood efficiency across its large portfolio of fields undergoing secondary recovery via waterflooding. It was observed that, in most of the waterflood developments reviewed, there was a lack of understanding of the reservoir operating limits, and the concept of an optimum operating target by subsurface engineers. A methodology is developed to estimate the optimum reservoir operating pressure target to maximize throughput and visualize the reservoir operating envelope of waterflooded reservoirs by identifying the reservoir offtake and intake limits which are calibrated with actual field data. The approach is based on identifying the reservoir Intake and Offtake limits and plotting the Inflow & Outflow Performance Relationships derived from average well performance data within a pattern to visualize the reservoir operating envelope. It utilizes the well productivity index equation to build the relationship between the reservoir limits to derive the Optimum Reservoir Pressure target at which maximum offtake and intake at an instantaneous voidage replacement ratio (iVRR) of ∼1 can be achieved within the defined limits (i.e., Maximum Throughput). The workflow and method are described in detail to allow the readers to replicate approach.
The methodology has been assessed on several waterflood development projects across PDO covering clastic and carbonate reservoirs with varying properties, well types (vertical and horizontal) and pattern types. The workflow was found to provide engineers with a deeper understanding of the reservoir operating limits for a given pattern that allows them to quickly assess pattern performance against benchmarks and make well informed decisions. It allows for setting a target reservoir pressure with a technical basis that is calibrated with actual field performance and can be continuously reviewed as fields mature. It was also observed that the method provides for an assessment of the efficiency of pattern configurations where producer to injector ratio is greater than 1, and a parameter sensitivity analysis to support in well optimization decisions. Understanding the reservoir operating envelope is critical in waterflood developments to optimize a pattern's well offtake and intake, maximize reservoir throughput, and optimize pattern configuration.
The novelty of this method is to standardize an approach across the company to identify the Reservoir operating limits by outlining the workflow to define and visualize the operating envelope for a given pattern that is calibrated with actual field data and derive the optimum reservoir operating conditions (rates and pressures).
