Abstract

Eliminating or controlling lost circulation during drilling or cement operations is a costly and time-consuming process. Traditional treatments include lost circulation materials (LCM), cement, crosslinked polymers, dilatent slurries, reinforcing plugs, and silicate systems. The general practice is to cure the losses before proceeding to the cementing operation. The mixed results of such treatments plus the fact that cementing operations sometimes proceed even with partial or total losses have led to the development of a new advanced-fiber cement system (AFCS). This paper will discuss the properties and the mechanism of the AFCS and its successful applications as a solution to lost circulation in the Middle East and the Far East.

AFCS forms a fibrous network across highly permeable formations, induced and natural fractures, and vugular formations to prevent and stop the losses during remedial or primary cementing operations. Unlike conventional fibers that normally are difficult to disperse in the cement slurries and tend to plug surface and downhole equipment, AFCS does not suffer from such drawbacks.

Laboratory tests have shown the effectiveness of AFCS in plugging different hole sizes. The efficiency of this system was enhanced in the laboratory when combined with high-performance lightweight cement slurry (HPLW), an optimized particle size distribution system. Several jobs in Abu Dhabi showed substantial success rates compared with traditional lost-circulation treatments. This was confirmed by cement returns to surface and cement coverage across the lost-circulation zones.

Other field locations utilized AFCS in cement plugs, top jobs, and primary cementing operations through different float equipment, liner hangers, and even coiled tubing without any plugging problems.

Introduction

Lost circulation is defined as the total or partial loss of drilling fluids, completion fluids, or cement slurries into highly permeable formations (e.g., sandstones), cavernous formations (e.g., limestones), and natural or induced fractures (e.g., dolomites) during the drilling, completion, or workover operations. Fighting lost circulation is a costly and time-consuming process with several possible consequences such as stuck pipe, well control incidents, the need to run additional casing strings, formation damage, and poor zonal isolation caused by poor cement coverage.

There are numerous lost-circulation treatments available in the drilling industry. These systems can be summarized into two main categories. Conventional treatments are the ones that include a combination of granular, fibrous, and flaky materials that are mixed with either the drilling fluids during the drilling phase or with the cement slurries during the drilling or the primary cementing phases. Specialized treatments include systems such as specialized cements, dilatent slurries, reinforcing soft or hard plugs, crosslinked polymers, and silicate systems that are also used either during the drilling or the cementing phases.

The success level for curing lost circulation is highly dependent on key factors like the durability and the temperature limitation of the treatment, the treatment placement, and the impact of the treatment on the producing formations. The common technique is to cure the losses before proceeding with the cementing operation; however, there are numerous cases in which losses are encountered just before or during the cementing operations. Some of the traditional treatments for these scenarios have been spotting cement plugs in the open hole during the drilling phase or cementing with a lightweight cement system that includes LCM during the cementing phase. The success level for these kinds of treatments varied from one case to the other and there was a need for a new type of treatment.

Fibers in Cement Slurries

Fibers have been used extensively in the construction industry as a way of reinforcing concrete. The main purpose of these fibers is to increase concrete toughness and prevent cracks from further propagation.

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