RIASSUNTO
Abstract
The majority of the reservoirs in a study field in Indonesia are gas producers with water. The average production is more than 650 MMscf/D with 11,000 BWPD. The reservoirs are characterized as multilayered sandstone water-sensitive formations with permeability ranging from 0.1 md to 2 darcy. The measured depths (MD) of the perforated producing zones extend from 9,400 to 11,100 ft, with an average reservoir bottomhole temperature of 240°F (115°C).
The study field has experienced significant water breakthrough in recent years, which has led to a drastic reduction in the total gas production per well. To increase gas production, it is required to reduce the water-gas ratio (WGR) to prevent the water-source reservoirs from killing the other producing layers and to stabilize the well's flowing conditions. This could be achieved by shutting off the undesired water production. The main challenge of the study field is the number of reservoirs opened per well (>30 perforated reservoirs), with short distances between the perforated zones. Mechanical isolation was impossible in these cases because it would create restrictions during future interventions.
A multidisciplinary group developed an innovative solution to shut off the water in these wells. The solution included a straddle system that consist of an inflatable retrievable bridge plug used as bottom isolation and an inflatable packer conveyed with coiled tubing (CT) as upper isolation, combined with a chemical water-shutoff treatment. The system was successful in shutting off the watered-out sands while keeping the upper reservoirs producing to date. This CT placement technique opened many opportunities for selective water-shutoff treatments of middle zones. This paper discusses the methodology of the job design, with a detailed operation sequence and results obtained from the field, including production results of some of the treatments pumped in the study field.
Introduction
The operator's main objective for the study field was to increase hydrocarbon production and to secure remaining gas resources from other perforated reservoirs, and the reservoirs that will be perforated in the future, by permanently shutting off undesired water production. Some wells in the field have more than 30 opened reservoirs, which introduces many challenges to the water-isolation process. These challenges have been overcome with the introduction of chemical treatments that can be combined with mechanical methods to effectively isolate water zones without leaving a restriction in the wellbore.
A variety of mechanical water-shutoff methods are currently available on the market for controlling undesired water flow in wells with multiple sets of perforations. One of the most common is to run a casing patch to mechanically isolate the perforated interval. However, in many cases, setting the casing patch would create limited access to the lower reservoirs for future well intervention by adding restrictions in the wellbore and reducing the internal tubing size. This also is not feasible in some cases because of the limited length of the perforated interval, which could be shut off by casing patch (around 6 m); meanwhile, the target-zone thicknesses are usually longer than 10 m. The dogleg severity of a well deviation also limits the possibilities of running a casing patch successfully.
The introduction of chemical methods provided a new means to isolate the water without having to deal with the challenges previously discussed. The chemical methods range from cement slurries to water-based polymer systems. Using a cement squeeze to isolate the perforated interval or an entire wellbore is the earliest method, but the drawback of using this method is there will be a need to drill out cement left in the wellbore, which can be costly, time consuming, and possibly damage another open zone with drilling fluid.