Abstract

Monitoring the performance of the Kuparuk River Unit waterflood at a multi-well, pattern level is a critical part of field operations. The reservoir performance analysis optimizes allocation of injected fluid, helps identify well work and infill drilling opportunities, supports reservoir management strategies, and provides a basis for development planning. Faulting and stratigraphy of the reservoir make it difficult to determine areal and vertical allocation factors for fluids in the surveillance patterns; therefore material balance calculations are required to judge their validity. The problem is exacerbated by the number of patterns analyzed and the need to share intermediate results between all of engineers that need to be involved in the process.

To help solve the problem, a suite of programs for interactive pattern material balance was developed. The program suite includes a principle material balance calculation application along with several ancillary programs for interactive database updates and post-processing.

The program suite allows engineers to interactively change input parameters and review material balance results. Internal checks ensure consistency throughout the field. The programs are fully integrated with a large central relational database which includes tables for areal and vertical allocation factors, production, injection, and static pattern information.

Introduction

The Kuparuk River Field is located west of the Prudhoe Bay Unit on the North Slope of Alaska. The field is a highly faulted reservoir with an areal extent of over 200 square miles. The field is under active waterflood with some areas also under immiscible or miscible WAG (water, alternating with gas) flood.

A formal review of reservoir performance at the pattern level is done on an annual basis. The review includes defining patterns and allocating fluids produced from or injected into the patterns. This is followed by a comprehensive review of the performance on a pattern-by-pattern basis and rate forecasts. The review is necessary to help identify workover and infill drilling opportunities to optimize the waterflood It is also required to help with operational considerations such as allocation of injected fluids throughout the field.

The validity and usefulness of the surveillance review is highly dependent on accurate allocation of production and injection to each pattern in the Kuparuk River reservoir. This is a difficult problem because over 600 patterns in 2 zones are analyzed. The process is led by a team of five to six engineers. An additional 15 to 20 engineers and geoscientists are involved in defining patterns and evaluating allocation factors. Because of the large number of individuals involved and the large amount of data, a group oriented solution was required in order to achieve consistency across the field. Internal data checks were also required so that wells could not be over or under allocated and to accurately account for all fluids.

History of Software Development Efforts. Several computing solutions have been explored. The first software solution was a mainframe material balance program tied to SAS databases. Iterations required editing ASCII text files and overnight batch runs to update databases followed by a batch processing for pattern analysis. Visualization consisted of batch programs that submitted plots to central printers, often with half-day turnaround times. A major advantage of the system was its use of a centralized database and enforced consistency. The disadvantages of long turnaround times and other difficulties within the mainframe environment made the process inefficient and manpower intensive.

As personal computers became more popular, much of the process was ported to spreadsheets. The analysis process consisted of downloading data from mainframe databases into a text format that was read into the spreadsheets. Engineers manipulated and modified the data within the spreadsheets to perform individual pattern analyses. The process was somewhat more efficient in terms of manpower, but consistency was nearly non-existent.

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