Lost circulation is one of the main causes of nonproductive time during drilling and impacts the success of cementing operations. Losses into the reservoir not only impact drilling, they potentially impact the reservoir, due to influx of quantities of drilling fluids that are potentially damaging, or will influence the production rate. Existing solutions are based mainly on particulates, which often are added to drilling fluids to plug fractures or to build up filtercake to cure fluid losses. When particulates are applied for curing losses in reservoir sections, it is desirable that the plugging materials maintain stability for sufficient time to allow well completion but eventually self-degrade to leave undamaged formation for future hydrocarbon production. The main challenges are the design of the lost-circulation material to cure losses into fractures of various widths and to provide plug stability and cleanup within a desired time frame over a broad bottomhole temperature range.Fibers have shown good fracture-plugging behavior. Parameters affecting fiber performance include, but are not limited to, fluid viscosity, fiber concentration, fiber geometry, flow rate, effect of the wall, and fracture width. To effectively apply fibers as lost-circulation applications, a novel, fiber-laden fluid was designed for easy preparation on surface, allowing compatibility with bottomhole assemblies (BHAs). The decrease in velocity inside the fracture enables fibers to bridge and then plug the fracture, thus regaining circulation. The fibers are specially designed to degrade in an adjustable time frame sufficient to ensure plug stability until the well is completed. With time, the plug undergoes further degradation, leading to nondamaged formation for production.This novel degradable solution has been successfully proven during field trials in various drilling scenarios ranging from severe to total losses with effective and efficient loss mitigation, without issues on placement through BHA and bit nozzles, and mitigating further reservoir damage.
A nanotechnology-based sealing fluid was developed to solve compromised integrity in pathways too small, smaller than 120 μm, for conventional methods such as cement squeezes. Well integrity and environmental stewardship are at the forefront of our industry's relation with the public as oil and gas fields continue to encroach toward urban centers and the places we live and work. This push towards improved well integrity and a growing number of mature wells requires new and novel technologies and materials to achieve our goals. The nanotechnology-based sealing fluid is capable of penetrating small gaps, as small as 20 μm, and seals through a reaction from either set cement or brine in the leak path. Candidate wells were selected based on very low injectivity rates that conventional remediation techniques could not tackle. Six candidate wells were selected, and of them, two were selected to cure a leaking gas microannulus causing sustained casing pressure and four were selected to cure a pinhole leak in the casing to pass the Texas Railroad Commission H-5 pressure test. For the pinhole leak, the nanosealant was placed across the leak point, and pressure was applied at surface continually until leakoff was minimized. The leaking gas microannulus was squeezed from surface until the leakoff was eliminated. The nanotechnology-based sealing fluid was successful in each case. For the leaking microannulus wells, hesitation squeeze schedules were applied, and both leaks were sealed with a projected penetration greater than 500 ft. These wells were then tested with light detection and ranging (LIDAR) to ensure no gas leaks were occurring at surface after the treatment. For the candidates selected with casing leaks, all passed the regulatory Texas Railroad Commission H-5 pressure test and were put back into service. Three of the wells resulted in a final pressure drop of 0 psi/min based on the hesitation squeezes, and the other one well resulted in a pressure bleedoff reduction more than 25 times the original bleedoff rate. The activation mechanism based on contact with annular materials is a significant breakthrough in squeeze operations because it removes all complexity from the fluid design, which historically required extensive laboratory testing. It also removes time-based boundaries on placement, and ultimately, it eliminates or reduces the drillout time compared to conventional or resin applications. Conventional remedial placement techniques can be used with the sealant, thus further simplifying the job execution. This combination of simplified execution techniques and the lack of necessary laboratory testing and well condition input allows for a quick fit-for-purpose implementation as problems arise, which saves both time and money.
Currently, hydraulic isolation of wells drilled with nonaqueous fluids (NAFs) relies heavily on the elimination of mud from the annuli before the placement of cement. Failure to expel all NAFs will result in residual fluid channels that will compromise well integrity and can even serve as nonproductive communication pathways during subsequent stimulation treatments. To mitigate this risk, an interactive cementing system is presented that is designed to reduce conductivity of the residual mud channels. Although mud removal remains an integral part of the cementing process, this new cement formulation was developed to improve zonal isolation in the case of poor mud removal. The unique cement system reacts with the hydrocarbons present in NAFs, leading to a reduction of channel permeability and mobility. This significantly improves the likelihood of hydraulic isolation. Specialized testing protocols were developed to enable the demonstration of the capabilities of this new system. In addition, API testing methods and analytical techniques were used to optimize the slurry. The development of the new cement system focused on the optimization of the active component concentration to give a favorable interaction with NAF, and at the same time, minimize the effect on cement rheology and mechanical properties. Procedures developed in-house demonstrated that the new system effectively reduces hydraulic conductivity of microannuli as well as channels up to several tenths of inches in size. Zonal isolation laboratory experiments were extrapolated to predict whether the modified channels can withstand the range of differential pressures typically seen between neighboring fracturing stages. This is the most critical operation that the cement sheath would be subject to. Field tests are on-going at the time of writing this manuscript, and the preliminary results will be presented and discussed in this paper.
Effective and verifiable zonal isolation is an increasing industry concern, especially in the strict regulatory environment of California. Unconsolidated formations in the Midway-Sunset field of the San Joaquin Valley have proven to be a challenge for conventional well construction designs to meet job objectives. Several root causes for a failure to achieve verifiable zonal isolation were found, including losses due to weak formation, logging issues associated with low-density cement, and technical challenges of logging in what is known as the air sands, an unconsolidated sandstone formation with dry pore space. Incremental improvements in the well construction design of the Midway-Sunset field developed several best practices. Low-density thermal-resistant cement systems with lost circulation materials were implemented to improve top-of-cement and cement-to-surface success rates. In addition, modifications to the cement system design were made to improve rheological properties to reduce equivalent circulating density (ECD) while maintaining a high solid volume fraction (SVF). The focus of this paper is the addition of a spacer train with a specialized silicate solution that was applied to solve two concerns in the field: losses across the unconsolidated formations and the poor log response in the air sands. Since the implementation of the best practices, significant improvements in verification of effective zonal isolation have been achieved. In problematic wells, those that incurred heavy losses prior to the cementing operation, the success rate of achieving cement to surface increased from 45% to 75%. This is the result of using lost circulation materials, reducing the density of cement systems while maintaining a high SVF and low fluid loss properties, and reducing ECDs through modified rheological properties. In addition, the specialized silicate spacer train improved the response of the cement bond log (CBL) run in these wells. Interpreting a CBL in the Midway-Sunset field has been historically difficult due to the air sands. The dry pore space of this formation is known to dehydrate cement slurries. Dehydrated slurries may be one factor leading to the formation of a dry microannulus which affects the response from a CBL. The specialized silicate spacer train performs two important roles in solving this problem. First, the specialized silicate spacer train enters the pore space and unconsolidated matrix of the formation. Upon mixing with the chloride activator, the silicate solution reacts quickly forming a rigid gel and thus preventing the bulk losses of cement slurry to the formation. In addition, this silicate spacer inhibits fluid loss from the cement slurry that could dehydrate the slurry and cause a microannulus. Over 200 wells have been drilled and cemented in the Midway-Sunset field since the implementation of these best practices, and improvements have been seen throughout the well construction process from the initial placement of the slurry through the logging evaluation.
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