Application of Flux-Based Sand-Control Guidelines to the Na Kika Deepwater Fields

Abstract

Summary The Na Kika offtake guidelines were developed jointly by Shell and BP using a blending of recent sand control operational methodologies from each company. This paper focuses on the use of the BpfluxTM guidelines, which give maximum safe operating rates for sand-control completions and allow wells with excellent completion quality to produce at twice the rate of wells with lower completion quality. Before the Na Kika field started up, completion quality was estimated by reviewing 20 different elements of completion design and operations. These estimates were used to set the initial offtake limits for each zone. As the wells started producing, pressure buildups were used to measure the actual completion quality (skin), and the maximum operating rates were adjusted accordingly. By use of this methodology early in the field life, the field could be brought up to targeted production rates without unnecessarily compromising long-term sand control reliability. As the field matures, opportunities will be identified to extend the production plateau, which will provide an incremental production impact. Finally, later in the field life, the number of workovers required is expected to be reduced, which will provide an additional cost saving from using these guidelines. Introduction The Na Kika development is in the deepwater Gulf of Mexico (Fig. 1), with 12 subsea wells that tie back to a host facility with a production capacity of 130,000 barrels of oil per day (MBOPD) and 500 million cubic feet per day (MMCFD) of gas. There are six separate fields that tie back to the host, which makes this development unique because there is no large field that justified the host on a standalone basis. With the exception of the Coulomb field, which was developed after the scope of work in this study, Shell and BP are equal partners in the Na Kika development. All the wells have sand control completions, two are openhole horizontal wells with gravel packs, and the remaining eight wells are cased holes with frac packs. As with any deepwater and subsea development, long-term reliability of each well is critical to project success. Over the past few years, well operating guidelines for sand control have moved away from drawdown-based limits and are now based on velocities at various locations in the completion. In particular, two recent studies both offer powerful new methods for safely operating sand control completions. Wong et al. (2003) discuss two velocity limits: one is the perforation velocity at the casing inside diameter, which, if too high, leads to destabilization of the annular pack. The second is the velocity at the surface of the screen, which if too high, causes screen erosion failure. They also present a surveillance-tool methodology to monitor well cleanup during the startup portion of a well's life. Tiffin et al. (2003) present the results of a large database used to develop empirical guidelines for safe operation of sand-control completions. They introduce a flux-based c-factor, which is directly proportional to the perforation velocity and allow wells with excellent completion quality to produce at twice the rate of wells with unknown or poor completion quality. The focus of this paper is on the application of these BpfluxTM guidelines to the Na Kika development. This paper begins with a brief overview of the BpfluxTM guidelines, highlighting the importance of a high-quality completion. It proceeds to discuss how these guidelines were incorporated into the Na Kika offtake guidelines. Two planned pressure buildups performed early in the well life to document the skin for each well are discussed and analyzed. The paper continues with examples of the use of pressure buildup (PBU) results and actual well drawdown data to increase the rates of wells using the guidelines. Use of these guidelines during the life of the field, particularly for wells with increasing skin, is also discussed. The paper concludes with a review of the actual Na Kika completion quality, examining which elements of the completion design and execution correlate with the measured skins. BpfluxTM Overview The BpfluxTM guidelines were developed by (Tiffin et al. 2003) using an extensive database of cased-hole and openhole sand control completions, primarily from the Gulf of Mexico and Trinidad. The rationale for developing these guidelines is made clear in Fig. 2, which shows the fate of 160 wells in the database. The vertical axis is the total drawdown, and each vertical colored bar represents a well. Green-colored wells had no sand production, yellow wells produced some sand, and red wells were erosion failures. Only wells with confirmed good-quality completions were included in the database; early-life failures caused by poor sand-control placement were excluded. First, Fig. 2 shows that there is no correlation between drawdown and well failures. Several wells with drawdown over 1,500 psi operate with no sand production, while one well with only 250 psi drawdown failed. Even the average values show no correlation, as the average drawdown of wells that failed is approximately 50 psi lower than the average for wells that produced sand-free. These observations led to the development of the BpfluxTM guidelines for cased-hole sand control completions, which are illustrated in Fig. 3.

Na Kika Field Experiences in the Use of Intelligent Well Technology to Improve Reservoir Management

“…If the reservoir skin increases then it is necessary to evaluate the impact of the skin on the flux limits of the completion (Keck, et al 2007). If the skin of the reservoir increases then to achieve the same production rate from the reservoir the drawdown pressure at the reservoir must increase.…”

“…Furthermore, proper application of the flux methodology (Keck et al 2007) based on reservoir production allocation data has avoided well failures and provided flexibility for production increases. Models are re-calibrated by running PBU twice a year or when predicted rate and well test rate do not agree.…”