Development of a Large-Bore Monobore Completion System for Gas Production

Abstract

Traditionally, monobore completion techniques have been able to provide operators with a high degree of flexibility for maintenance needs since the tubing imposes no restriction to any tool that may be deployed in the liner as sometimes happens when completions have tapered production strings. Unfortunately, the traditional monobore completion advantages may not be realized until later in the life of the well. While maintenance is always important, the general volatility of oil prices has forced the industry to target operational strategies that can also offer quicker returns on investment. Since the completion system discussed in this paper employs large-diameter production tubing, it provides the maintenance benefits of a monobore system but with added advantages that a large flow area can provide. The increased flow areaallows the number of wells to produce a given reservoir to be reduced andenables production rates to be increased, which in turn, reduces long-term operating expense since the reservoir can be depleted in a shorter period of time. The specific benefits of the large-bore monobore completion are as follows:No restrictions are imposed on productionProduction rates are maximizedGas turbulence areas are eliminatedNo restrictions on any service/intervention toolsTubing retrieval to the liner top is allowedFull access to the liner for squeezing or mechanical isolation of the perforations is allowedAncillary equipment requirements are minimized. Introduction Monobore completion techniques have continued to gain wide application in the industry.1,2,3 As the name suggests, a monobore completion configuration uses a production conduit with a uniform internal diameter throughout its entire length. This type of completion offers several advantages over traditional completion schemes; some associated with wellbore construction, others with remedial operations. The large monobore completion system discussed here provides traditional monobore advantages but maximizes each well's production rate, which improves the revenue stream early in the project. Foremost in the list of monobore design benefits is that the number of wells needed to develop a field is minimized. Fewer wells decrease operational and maintenance expenses for the life of the field, and each well can be produced at higher rates if needed to meet contract requirements for peak demand or if another well is shut in. In addition, wellbores without restriction reduce areas of gas turbulence, and thus, improve completion reliability. Significant design flexibility is possible since larger tubing strings can be used with a given casing program or smaller casing programs can be run with a given tubing string. Larger tubing sizes also reduce frictional pressure drop, allowing higher flowing tubing pressure at the same rate and giving increased deliverability. While the remedial advantages of monobore completions may not be realized until later in the project's life, their importance should not be under estimated, especially with larger tubing sizes. Compression can be delayed, and stimulation effectiveness can be increased since higher pump rates are possible. No restrictions are in place for any service or intervention equipment, expanding flexibility in remedial services. Finally, full access to the liner top allows easier squeeze or mechanical-isolation operations to be conducted. Since large monobore completions can obviously improve field development economics by reducing capital and operating expenditures, improve the early revenue stream for the project, and allow a greater scope of remedial operations to be considered, a 9–5/8-in. monobore completion system has been designed. A comparable 7-in. system with similar benefits and design features has also been developed. The discussion in this paper will focus on the development and economic advantages of the 9–5/8-in. system.