Improved Well and Reservoir Management in Horizontal Wells Using Swelling Elastomers

Abstract

Petroleum Development Oman (PDO) is producing substantial amounts of unwanted water or gas from most of its oil fields. To increase recovery from maturing reservoirs, PDO is developing the capability to detect and shut-off unwanted water and gas. Swelling elastomers have been deployed to segment horizontal wells in combination with surveillance and shut-off technologies. In beam pump wells dual wellheads have enabled logging while pumping. A key element to achieve improved oil recovery through well and reservoir management in a horizontal well is segmenting the well into different flow units. Swelling Elastomers (SE) are being deployed to enable segmentation. SE tool provides zonal isolation through the swelling of the elastomers when contacting produced water in the wellbore. In clastic reservoirs the completion philosophy has been changed from drilling minimum functionality wells to wells with closed-annulus completions that allow for surveillance and interventions. Surveillance is done in the drilling phase with under-balanced drilling and other open hole logging measurements. In the work over phase unwanted flow segments have been detected by logging while pumping coupled with greater integration of available reservoir data. Mechanical segment shut-off methods have been used. To date PDO has segmented more than 100 horizontal wells with swelling elastomers. In more than 20 wells suspected water producing feature were isolated at the initial completion stage and the rest were segmented based on reservoir flow unit characterization. After having proved that SE is delivering value in initial water shut off, the strategy is to prove a viable surveillance technique to identify water entry point in horizontal wells, and to develop several reliable water shut off (WSO) techniques depending on which segment's to be closed and if reversibility is required. To date more than one million barrels of oil have been realized as a result of the initial isolations as well as subsequent water shut offs. This paper is a continuation to the work presented in SPE paper number 91665 and will present case histories of the delivery and management of wells with swelling elastomer in clastic reservoirs in Oman. Introduction The South fields are located in southern Oman is in fact a group of six fields. Most of them are mature oil fields operated by Petroleum Development Oman. The fields produce medium gravity viscous crude with viscosity ranging from 200–550 cp. Reservoir pressure is maintained by infinite bottom water drive. The fields have been producing since mid 1980's. Initial fields' development was via vertical wells however, since the mid 1990's development has been primarily with horizontal wells. Production is from a combination of Aeolian and glacial sediments. Reservoir heterogeneity is high especially in the glacial Alkhalata reservoir. These fields accounts for more than 10% of total PDO production and is produced from almost 500 active wells. The current field water cut is about 93%. South field wells have different design. Almost all South field wells must have sand control. The horizontal reservoir section is about 350–500m long. The horizontal section may cross both reservoirs (Alkhalata and Aeolian Amin reservoirs). The horizontal section is drilled with a 61/8" drill bit and completed with stand-alone 4½" sand control liner using 200 micron wire-wrap screens (WWS) in open hole. This results in an open annulus between the sand control liner and the formation. More than 90% of well are artificially lifted via beam pump (BP) hence hindering accessibility due to surface units and rods. In the early development phases it was assumed that water production is simply a result of conning, and water is produced through matrix and all faults fractures are assumed to be sealing. However since the start of infill drilling in 1999, the new oil production has been historically dominated by high initial BSW levels and as of 2002 new wells produced cumulative average of three barrels of water for every one barrel of oil during their first year of production.

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