Openhole Gravel-Pack in Depleted GOM Reservoirs Achieved With Alternative Approach
Chris Carpenter_
This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 227908, “Successful Openhole Gravel Pack With Alternate-Path Technology in Depleted Reservoirs: A Mindset Change in Gulf of Mexico,” by Lehron Brune, Walker Shirley, and Brandon Vu, BP, et al. The paper has not been peer-reviewed.
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In Gulf of Mexico deepwater, most reservoirs are unconsolidated formation sands that require sand-control completion. Cased hole frac-packing historically has been the default technique. However, in many fields, prioritization of pay access across multiple stacked sand packages or across faults in the reservoir has driven the operator to evaluate the feasibility of openhole gravel-pack (OHGP) completions. This paper discusses the successful execution of two OHGP completions in two fields with depleted reservoirs.
Sandface Completion Selection and Design
Because both wells have a low fracture margin, shunted screens were required to ensure that complete packing in the fracture pressure was exceeded during the job execution. The openhole sections were drilled with synthetic oil-based reservoir drill‑in fluid to 8½ in. and underreamed to 9¼ in.
A 7⅝‑in. predrilled liner (PDL) was installed before running screens for mitigation against geomechanical loading onto the sand screens for the life of the well, and to enable the screens to be run in hole (RIH) in completion brine rather than conditioned mud. The PDL specifications included ½‑in. holes (312 per ft) giving a 20% flow area and were centralized in the open hole with bow‑spring centralizers. The bottom of the PDL assembly featured an indexing guide shoe, meant to enable conveyance to total depth (TD) in challenging hole conditions. The service running string included the setting tool assembly and 4½‑in. washpipe with float subs to enable holding the backside pressure with the managed-pressure-drilling (MPD) system for the trip in hole with the assembly.
The sand screens selected for this design were 12‑gauge, 4‑in., 2×2 shunted wire‑wrapped screens with a cross-connection dehydration system. The screens were centralized inside the PDL and were nonshrouded. A fluid‑loss‑control valve was included to provide fluid‑loss management post‑GP and an operational well barrier during installation of the upper completion. A 9⅝‑in. × 6‑in. GP packer and the service tool were designed to prevent swabbing throughout the entire operation, and enabled washdown capability during RIH. A comprehensive risk assessment was performed to evaluate every step of the operation.
Under MPD conditions, the system imposes a pressure differential across the valve. To address this, the bypass valve was redesigned to increase the shear rating from a standard approximately 500 to 1,500 psi.
Displacement and GP Carrier-Fluid (GPCF) Selection
Displacement Fluids.
The fluid train used to displace the mud from the openhole after running the PDL consisted of a base oil spacer, then a high-density push pill, followed by a suspension pill. A standard fluid train was used to displace the casing to filtered brine.