How to Make Sensitive Formations Produce Oil: Case Study of the Complex Laboratory Approach to Stimulation Fluid Optimization

The Bahrain field is one of the oldest developed oil fields in the Middle East, with over a dozen formations in production since the early 1930s. Currently, development of the shallow zones (<2,000 ft) of the Magwa and Ostracod formations is a challenge due to the unique complexity and extreme clay sensitivity. With previous fracturing attempts showing limited success, enhanced laboratory testing was undertaken to make fracturing treatments economic. Formation stabilization improvement is crucial in certain reservoir mineralogies, especially those with exposed shale streaks and high concentrations of clays that exhibit extremely high brine sensitivity. Lack of adequate stabilization of sensitive clays and shales risks the deconsolidation of those minerals into fines that may potentially damage the conductivity of the proppant pack in fracturing operations. Many problems associated with the use of water-based fluids in fracturing operations are caused by incompatibilities between the fracturing fluid and the shale minerals, resulting in a fines migration problem in the relatively low-permeability reservoir and a production decline after the fracturing operation. A scientific approach was applied to the selection of novel shale inhibitors to be used in fracturing applications. First, a laboratory testing program was followed to incorporate a new shale inhibitor into the fracturing fluid system. The fluid recipe was further optimized with a reduction in polymer loading, maximizing breaker concentration and ensuring fast shear recovery, because the stimulation design called for large-size proppant (up to 12/20 mesh) to be used in a low-temperature (124°F) environment. The laboratory results demonstrated that the new shale inhibitor significantly reduces alteration of the permeability of the treated core and improves shale stability. The new inhibitor was deployed in the field, as documented in several case histories. Production results of the treated wells demonstrated several-folds increase in production when compared to previously attempted proppant fracturing treatments. The pilot stimulation campaign proved the value of the laboratory research and brought on line two formations with large potential contribution to Bahrain's overall oil production. Although there is a substantial amount of literature on shale inhibition with water-based drilling fluid, the importance of the shale inhibition and the problems associated with shale reactivity during the fracturing operation remain largely unexplored. This paper presents the complex laboratory approach to stimulation fluid optimization in the Bahrain field. The novel solutions and comprehensive workflow description will benefit a broad variety of projects worldwide targeting water-sensitive or low-temperature formations that represent challenges to fracturing fluid selection.

Dry Powder Deliver of Friction Reducers: A Step Change in Slickwater Fracturing

Since the early development of unconventional resource plays, slickwater fracturing fluids have expanded rapidly and are now the most common type of fluid system used in the industry. Slickwater and viscosifying friction reducer (VFR) fluids consist of polyacrylamide (PAM) polymers and are typically delivered to location in a liquid form such as a suspension or emulsion in a hydrocarbon-based carrier fluid. Recently, advances in dry powder delivery operations have provided unique advantages over the liquid versions of FRs including cost savings and improved health, safety and environmental (HSE) aspects. This paper describes the dry powder delivery process and describes the advantages that this new technology has brought to field operations. The method involves delivering polyacrylamide powder for slickwater fracturing treatments directly into the source water on location, thereby eliminating the use of liquid polymer slurries or emulsions. Liquid friction reducers typically contain 20-30% active polymer loading, with the remaining volume being the carrier fluid to keep the polymer in suspension. By delivering 100% powder, several benefits are gained including elimination of truck deliveries of FR liquids to location, reduction of total chemical volumes by 70-80%, reduction of spill hazards, and lower overall chemical costs. Different powders are available for various applications including the use of fresh or produced water, and viscosifying or non-viscosifying polymers. The key technology for "dry on the fly" (DOTF) operations is the powder delivery equipment. Due to the different molecular structures between polyacrylamide and guar polymers, delivering PAM is more technically challenging than guar and requires much higher mixing energy to achieve proper dispersion and hydration. The delivery system described in this paper uses a unique technology which creates the necessary conditions for powder mixing and has been successfully applied on over 350 wells since early 2019, with over 7,000 tons of polymer delivered.

Mathematical Modeling of Polymer Loading Process in Extruders

Based on the state of the problem related to highquality and reliable insulation coating of high-voltage cables, the problems of mathematical modeling of pro-cesses in the loading zone and the delay of the polymer mixture in a single-screw extruder are formulated, which is crucial in terms of providing a high-quality insulation coating. An iterative numerical-analytical method for solving the corresponding nonlinear boundary value problems is proposed, based on the use of finite integral transformations in the spatial and temporal domains and their implementation.

Dual-Polymer Hydraulic-Fracturing Fluids: A Synergy Between Polysaccharides and Polyacrylamides

Summary As exploration for oil and gas continues, it becomes necessary to produce from deeper formations, and to meet the challenge of low permeability and higher temperatures. Unconventional shale formations are addressed with slickwater fracturing fluids, owing to the shale's unique geomechanical properties. On the other hand, conventional formations require crosslinked fracturing fluids to properly enhance productivity. Guar and its derivatives have a history of success in crosslinked hydraulic–fracturing fluids. However, they require higher polymer loading to withstand higher–temperature environments. This leads to an increase in mixing time and additive requirements. Most importantly, as a result of high polymer loading, they do not break completely and thus generate residual–polymer fragments that can plug the formation and significantly reduce fracture conductivity. In this work, a new hybrid dual–polymer hydraulic–fracturing fluid was developed. The fluid consists of a guar derivative and a polyacrylamide–based synthetic polymer. Compared with conventional fracturing fluids, this new system is easily hydrated, requires fewer additives, can be mixed “on the fly,” and is capable of maintaining excellent rheological performance at low polymer loadings. The polymer mixture solutions were prepared at a total polymer concentration of 20 to 40 lbm/1,000 gal at volume ratios of 2:1, 1:1, and 1:2. The fluids were crosslinked with a metallic crosslinker and broken with an oxidizer at 300°F. Testing focused on crosslinker/polymer–ratio analysis to effectively lower loading while maintaining sufficient performance to carry proppant at this temperature. A high–pressure/high–temperature (HP/HT) rheometer was used to measure viscosity, storage modulus, and fluid–breaking performance. An HP/HT aging cell and HP/HT see–through cell were used for proppant settling. Fourier–transform infrared (FTIR) spectroscopy, Cryo scanning electron microscopy (Cryo–SEM), and an HP/HT rheometer were also used to understand the interaction. Results indicated that the dual–polymer fracturing fluid was able to generate stable viscosity at 300°F and 100 s−1 as well as generate a higher viscosity compared with the individual–polymer fracturing fluid. Also, properly understanding and tuning the crosslinker to the polymer ratio generated excellent performance at 20 lbm/1,000 gal. The two polymers formed an improved crosslinking network that enhanced proppant–carrying properties. This fluid also demonstrated a clean and controlled breaking performance with an oxidizer. Extensive experiments were pursued to evaluate the new dual–polymer system for the first time. This system exhibited a positive interaction between the polysaccharide and polyacrylamide families and generated excellent rheological properties. The major benefit of using a mixed–polymer system is reduced polymer loading. Lower loading is highly desirable because it reduces material cost, eases field operation, and potentially lowers damage to the fracture face, proppant pack, and formation.