Scale Milling and Nipple Profile Recovery With Electrical Wireline - Case Histories From Successful Operations in the North Sea
Choosing the most economic sand-control system from the available options is a central component in field development planning. The choice of sand-control system depends on a number of factors such as production and sand-control performance, reserves recovery, reliability, ease of installation, and life-cycle economics. Logistical and health, safety, and environment (HSE) issues are also important, especially in areas with limited support infrastructure.
A key input to the process of sand-control-system selection is data on how the various systems compare in a given environment. Ideally, this comparison should be made over time to compare properly long-term performance and reliability. These data can be obtained only by analyzing existing installations fairly and objectively.
The Mokoko-Abana field is situated offshore Cameroon. It is a mature heavy-oil field with unconsolidated formations that require sand control from the onset of production. A wide variety of sand-control solutions have been used in this field, with varying levels of success and performance. Cased-hole internal gravel packs (IGPs), milled-casing openhole underreamed gravel packs (MCGPs), and cased-hole frac packs (CHFPs) have been used in vertical wells. Prepacked standalone screens (PPSASs), openhole gravel packs (OHGPs), and openhole expandable sand screens (OHESSs) have been used in horizontal and highly deviated wells.
Each of the completion options now has several years of production history. This allows their initial performance and their performance over time to be modeled and compared. The wells chosen for study were in the same sand body with an installation as close to perfect as possible. The MCGP had relatively good performance, as did the CHFP; unfortunately, however, the CHFP fractured into a water-bearing leg and only added water cut. The PPSAS had initially low mechanical skins, but its performance declined quickly. The OHGP had higher initial skins, but the rate of production decline was much slower. The OHESS had a very low initial skin with no impairment over the 5-year production period.
Mason et al. (2005) provide background information on the Mokoko-Abana field and look at the productivity performance of the PPSAS, OHGP, and OHESS techniques on initial completion and after 2 years of production. This paper follows on from that work and examines the operational, productivity, reliability, and economical aspects of the completion techniques over 5 years or more of production.
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