Abstract

Carbonate reservoirs are becoming increasingly more important for offshore oil and gas development. Typically, these reservoirs are produced using deviated or horizontal wellbores with production casing cemented in place to provide annular isolation. The reservoirs normally require acid stimulation treatments to connect natural fracture networks in the carbonate formation to enhance the productivity of the reservoir.

In order to perform the acid stimulation, perforating guns are first used to establish communications to the formation before stimulation, and then, composite plugs are set between stages to isolate one fracture stage from the next. The plug-and-perforate method will usually require multiple wireline intervention trips for the completion. Then, milling of the composite plugs is needed when the stimulation treatments have been completed. This increases completion cycle time and decreases operational efficiency.

This paper discusses a new completion process that has been developed to enhance the efficiency and safety of stimulating multiple target zones in a single wellbore in an offshore carbonate formation. This new process employs a permanently installed completion liner, and then, uses a retrievable service assembly with ball-actuated fracturing sleeves to enable stimulation through the completion liner. By using ball-actuated fracturing sleeves, completion cycle time can be reduced dramatically.

Then, a retrievable stimulation packer is used to allow the entire service assembly to be retrieved so that post stimulation can be performed with full-wellbore-ID access. The pulled service assembly can be run again at a future date for re-stimulation operations.

This paper discusses this new multi-zone completion process, and the tools used for the completion process will be reviewed. Efficiency gains and increased safety of this new process will also be highlighted to illustrate the potential for the positive economic impact that this new completion process can provide.

Introduction

Offshore carbonate reservoirs are becoming more popular formations for the development of oil and gas resources around the world. The reservoirs often contain interconnected natural fracture networks which can provide ready flow paths for oil and natural gas when effectively stimulated. When combined with good permeability, porosity and oil in place, carbonate reservoirs can make ideal candidates for exploration and development efforts. Many of these formations are produced through deviated or horizontal wellbores. These wellbores will typically use tradition perforating and stimulation methods across multiple zones to ensure that economic production levels can be reached. To stimulate these reservoirs, typically the goal is to connect the natural fracture networks to enable hydrocarbon production. This is done with either matrix acidizing or acid fracturing stimulation treatments across the multiple targeted zone in the formation. However in the offshore environment, traditional methods can often require months to finish the wellbore completion, stimulate the wellbore, and bring the well into production. This is due to the many intervention trips which are required during the completion process to perforate and isolate individual stages within the target formation.

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