Casing Drilling Manages Shallow-Gas Risk in Brownfield Redevelopment
Authors: Denney Dennis 
Published: February 2015

This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper SPE 156259, ’Managing Shallow-Gas Drilling Risk With Casing-Drilling Technology in Brownfield-Redevelopment Campaigns,’ by Hugo Costeno, SPE, Haakon Roed, SPE, and Ochuko Erivwo, SPE, Schlumberger IPM; Christie Usun Ngau, Petronas Carigali; and Andrew Harris, Tesco, prepared for the 2012 IADC/SPE Asia Pacific Drilling Technology Conference and Exhibition, Tianjin, China, 9-11 July. The paper has not been peer reviewed.

Casing drilling was used to optimize drilling of the tophole section in the Phase-1 wells of the mature Samarang field redevelopment campaign. Lost-circulation and stuck-casing incidents in the surface section had occurred in previous campaigns, and casing drilling was identified as a solution to mitigate these problems. This study focused on the casing-drilling application to reduce the risk of a shallow-gas blowout.

Introduction

The objective of redeveloping the Samarang field was to implement enhanced oil recovery (EOR). The field is in Malaysia, offshore Sabah, in the South China Sea. The field was discovered in 1972, and commercial production started in 1975. New wells were drilled in subsequent revisits in 1986, 1991, and 1998, and a workover and sidetrack campaign took place in 2002. Samarang reservoirs are at depths of 1,500 to 8,000 ft and comprise a series of alternating sand, silts, and clays. Part of the field lies underneath a shallow reef with a water depth of 30 ft.

The redevelopment plan had two phases. Phase 1, completed in 2011, included one sidetrack well from Platform SMDP-B (in 156-ft water depth) and four new wells, of which two are standalone and two are conductor-sharing wells drilled from Platform SMJT-F (in 33-ft water depth). Phase 2 was implementation of the EOR plans and included drilling infill producers and injection wells on seven platform revisits along with upgrading production facilities.

For Phase 1, the surface section of the four new wells was planned as a 16-in. hole, casing drilled with 13⅜-in. casing. Casing-drilling technology was chosen to optimize the drilling time and to reduce the risk of mud losses, hole instability, and stuck casing—problems reported in previous Samarang drilling campaigns and that, in some cases, forced setting the casing shallower than planned. Also, previous experience suggested that casing drilling would prevent problems with the conductor-sharing wells.

Ensuring that the casing is set at the planned depth became particularly important because of the simplified casing design used in Phase 1. The typical casing scheme for previous wells in the field used an 18⅝-in. surface casing set at approximately 1,000 ft, followed by the 13⅜-in. intermediate casing set at approximately 2,000 ft, and then the 9⅝-in. production casing to well total depth (TD).

The simplified casing design consists of a 13⅜-in. surface casing set at approximately 2,000 ft, followed by the 9⅝-in. production casing to well TD. Fig. 1 shows the simplified casing scheme that omits the 18⅝-in. casing string.