TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThe primary objective of cementing an oil or gas well is to provide good zonal isolation between different formations that have been penetrated by the wellbore. Cementing across weak formations with a low fracture gradient usually leads to poor cement coverage, which makes zonal isolation difficult or impossible.Abu Dhabi Company for Onshore Oil Operations (ADCO) recently had this problem in the water-bearing Palaeogene and Cretaceous carbonate formations that extend across all United Arab Emirates fields and the Gulf region. Several techniques have been used in the past to bring high-quality cement up to surface to protect casing from corrosive brines. These techniques include using multistage tools, pumping conventional lightweight cement to execute the cementing operation, and performing a remedial, top-down cement job after completing the primary cementing operation. Mixed results demonstrated the limitations of these techniques.Today, with a better understanding of the problem of cementing in these formations, a unique, cost-effective process has been developed to ensure that cement coverage goes up to surface. Essentially, it combines a sequence of three slurry systems, including a novel, ultra-lightweight cement technology, to defeat the severe lost-circulation problem and achieve complete zonal isolation. This paper describes the design and results obtained from the successful application of this new process to cement casings in formation where severe lost-circulation problems are likely to occur.

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThe primary objective of cementing an oil or gas well is to provide good zonal isolation between different formations that have been penetrated by the wellbore. Cementing across weak formations with a low fracture gradient usually leads to poor cement coverage, which makes zonal isolation difficult or impossible.Abu Dhabi Company for Onshore Oil Operations (ADCO) recently had this problem in the water-bearing Palaeogene and Cretaceous carbonate formations that extend across all United Arab Emirates fields and the Gulf region. Several techniques have been used in the past to bring high-quality cement up to surface to protect casing from corrosive brines. These techniques include using multistage tools, pumping conventional lightweight cement to execute the cementing operation, and performing a remedial, top-down cement job after completing the primary cementing operation. Mixed results demonstrated the limitations of these techniques.Today, with a better understanding of the problem of cementing in these formations, a unique, cost-effective process has been developed to ensure that cement coverage goes up to surface. Essentially, it combines a sequence of three slurry systems, including a novel, ultra-lightweight cement technology, to defeat the severe lost-circulation problem and achieve complete zonal isolation. This paper describes the design and results obtained from the successful application of this new process to cement casings in formation where severe lost-circulation problems are likely to occur.

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractLong-term zonal isolation of gas reservoirs is a difficult problem. This paper summarizes the implementation and evaluation of a new sealant system designed to overcome this problem by preventing formation of a microannulus across the gas zone. A case history of its use in a well in the United Arab Emirates demonstrates the successful application of the flexible, expandable sealant material to prevent microannulus and maintain cement sheath integrity in the production casing section.In one well, a conventional cement slurry formulation was used for the 9 5/8-in. section. The section was then tested to 3,000 psi pressure. Cement-bond logs showed clear deterioration of cement sheath quality behind the casing. A similar result for upcoming casing sections was a concern, so the sealant was redesigned to accommodate downhole stresses across the interval. The new design, which was used in the 7in. liner section in the same well, enabled mechanical and expansion properties to be engineered to withstand downhole stresses and minimize the debonding effect. After successful isolation in the first well, the flexible, expandable sealant material was established as standard practice in similar wells.

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