Using Cement -Through Completions to Improve Productivity and Safety in Short-Life Wells.
Authors: Eag-Ark Pasook , Chapman Walt , Orchard Anthony , Lewis Keith 
Published: October 2008

Cemented monobore wells offer operators an economically viable method of completing wells with life expectancies of three to five years. These wells have become the mainstay in the Gulf of Thailand and are prevalent throughout the Asia Pacific Region. The concept of disposable wellbores is also growing in popularity in other Regions worldwide. Because they preclude the use of packers and positive seals, disposable wellbores have, until now, posed a problem with regard to environmental impact and personnel safety. Additionally, because industry-standard gas lift devices are not cement tolerant, there has been no reliable method to gas lift these wells as production levels decrease.

Introduction

Throughout the oil and gas industry, focus is turning to economical methods of completing wells that in some cases would not be feasible, due to high completion cost. A prime example of wells with marginal economics is prevalent in the Gulf of Thailand. Common completion practice in this area is to complete the well in two stages. First, the tubing is cemented in place without use of a packer. Once this step is complete, the operator must then recomplete by cutting above the cement and rerunning completion strings with all the necessary equipment. This process is not only time consuming, but is also dependant on the integrity of the cemented portion of the first stage. A more fit-for-purpose completion system for disposable wellbores would include all the equipment necessary to safely and economically complete these wells. This system would also need to be a true monobore, one-trip completion that would allow cement to be pumped offline, freeing up the rig to move to another location on the platform. This completion system would eliminate 18 to 24 hours of rig time, which would offer a considerable cost savings. Components of this one-trip monobore system would also need to function properly following the cementing operation. These capabilities currently exist in the Mono-Trip CemenThru? completion system. This system relies on specifically designed cement tolerant components. This system is currently being used in the Gulf of Thailand.

Mono-Trip CemenThru Completion System

Completion Design.

The Mono-Trip system is based on a true monobore design with one-trip capabilities. More importantly, the system will operate as intended after cement has been pumped through each of the components. Pressure cycles are utilized throughout the completion to operate the various components.

A major factor in the design of this system involved fluids dynamics research. This research allowed a better understanding of how various fluids reacted under these conditions. To ensure that residual cement would be eliminated, turbulent flow was simulated. This simulation was performed using current component design, and the conceptual design of the new Gas Lift Mandrel. As depicted in Fig. 2), the modifications to the existing design created the turbulent flow characteristic required. The introduction of turbulent flow creating areas would in fact enhance the washing characteristics during the cement pumping operation. Another important factor of this simulation was the research as to whether the introduction of these turbulent flow areas would reduce the efficiency of the system during normal production.