Multi-zone Completion Design For Long Horizontal ERD Wells In Al Shaheen Field

Abstract

Maersk Oil Qatar AS, under the Exploration and Production Sharing Agreement with Qatar Petroleum, operates the Al Shaheen field, Offshore Qatar. In order to maximise recovery from the shallow and thin reservoirs, long horizontal ERD wells have been drilled in both, radial and line drive patterns with alternating producers and injectors. Recently, long horizontal wells pushing the limits of surface-controlled multi-zone completions in the reservoir were planned, drilled and completed. To achieve maximum reservoir contact, pre-drilled liners with open hole isolation packers were installed from the production casing shoe to TD (~6,800 ft to ~29,300 ft MDRT, ~3,450 ft TVDRT at 90° inclination) in multiple runs. The completion was installed to facilitate selective control of each of the 3 zones using surface controlled valves. The inner completion string was run to 22,985 ft by segmenting the completion string into 2 runs. This was achieved by having the lower section run on a drill pipe running string with a swivel to facilitate rotation of the running string to get to depth. The upper completion with multiple control lines was installed using floatation technique (~8,000 ft tubing length floated). One of the wells was subsequently acid stimulated using the Maersk Oil Patented controlled acid jetting (CAJ) technique. The objective of this paper is to share the installation experiences, detailed analysis, procedures used and lessons learnt completing these multi-zone wells. The paper also outlines procedures to establish initial conditions (using calculation spreadsheets to verify WellCat simulations), and then calculate all possible load cases expected during life of the well by using tri-axial design approach. A detailed analysis has been compiled to evaluate tubing length change, tubing-to-packer forces and casing-to-packer forces. The selective zone stimulation load case is analysed in detail. A detailed analysis of forces v/s limiting force envelopes for the tubing, packers and accessories for multi-zone completion has also been demonstrated. Introduction The Al Shaheen field has been under development since 1992 when Qatar Petroleum entered into an Exploration and Production sharing agreement with Maersk Oil Qatar AS as the Operator of the field1 (Fig. 1). The Al Shaheen field is located on the central axis of the Qatar Arch, some 70 kilometers North-East of the Qatar peninsula. It comprises of thin, stacked reservoirs (Fig. 2) mainly carbonates with low permeability. The aerial extent of the Al Shaheen field accumulations is substantial which requires a large number of wellhead platforms to develop the field. Moreover, due to relatively high oil viscosity vertical wells were found to be unable to sustain natural flow and gave low productivity with artificial lift. Therefore, the field is being developed with long horizontal wells drilled and completed from nine platform locations. The length of these horizontal wells has pushed the limit of directional drilling technology (Fig. 3). EOR techniques such as gas injection have been implemented in an effort to evaluate the scope for incremental field oil recovery2. The next step in this effort is to implement water alternating gas injection (WAG). Zone isolation is of primary importance for such WAG wells, which was the driver for installation of multi-zone completions with open hole isolation. This paper describes the planning, design and execution of drilling and completion of two pilot WAG wells that entailed a three zone completion with open hole isolation packers and selective completion.