Filter-cake cleanup in open-hole gravel-pack completions has traditionally involved several stages: gravel-packing, pulling out of the hole with the work string, running in hole with production tubing, running in hole with coiled tubing, circulating the excess carrier fluid from inside the base pipe and spotting a breaker solution. Furthermore, in cases where removal of both the polymeric components and the CaCO3 bridging agents is necessary, an enzyme or an oxidizer soak has typically been followed by an acid treatment. This process is time consuming and costly, in addition to being non-optimal in terms of uniform cake-cleanup in long open-hole completions, due to rapid reaction between acid and CaCO3 particles. Recently proposed simultaneous gravel-packing and cake-cleanup method incorporating breakers into the gravelpack carrier fluid have been demonstrated to be an efficient technique through more than a dozen field applications, as evidenced by higher productivity compared to offset wells completed with conventional techniques. Because of the inherent risk in simultaneous gravel-packing and cake-cleanup with water-packing technique, carrier fluids containing breakers for filtercake removal have been used in conjunction with shunt-packing, which has been demonstrated through both field applications and large-scale yard testing not to rely on either the filter-cake or the formation properties. However, because shunt technique relies on viscosity for gravel placement, application of the simultaneous gravel-packing and cake-cleanup technique with polymer-free visco-elasticsurfactant (VES) carrier fluids has been limited to wells requiring a density of about 9.8 ppg (for circulating packs) and a bottom hole circulating temperature less than 200°F. In this paper, we present new surfactant formulations, which have unique chemistry that allows them to form visco-elastic surfactant solutions in high-density brines and remain stable at elevated temperatures. Densities up to 13.8 ppg with a rheological profile suitable for shunt-packing at bottom hole circulating temperatures exceeding 250°F are achievable with this new surfactant, covering a large majority of the gravelpack applications. It is further demonstrated that this new surfactant system does not only allow the use of certain chemicals that can be used for CaCO3 dissolution in conjunction with a gravel-pack process, but also requires these chemicals as co-surfactants in order to develop a visco-elastic structure. In addition to discussion of the unique chemistry of this VES formulation, data pertaining to proposed gravel-pack applications are presented. These include rheology, gravel suspension properties, filtercake dissolution characteristics, and retained permeabilities. A field case history utilizing the new VES fluid incorporating filter-cake cleanup chemicals is also detailed.

An additive consisting of acrylic co-polymers, polyvinyl alcohols, polyvinyl acetates, polyvinyl versatates, butyl maleates, and polyvinyl pyrrolidones is considered as a fracture efficiency modifier (FEM) for inclusion in fracturing fluids for tight gas (0.001 to 0.5 mD). The chemical nature of the fracture efficiency modifier improves fluid efficiency, promotes cleanup, enhances gas production, and increases the effective fracture length. Although conventional thought suggests that fluid efficiency is not a controlling parameter in tight gas treatments, this work suggests it can be critical to enhancing well productivity. Lab studies support the field trends in regards to cleanup and fluid efficiency. A modified method for evaluating fluid loss tests provides more realistic values for wall building coefficient and spurt that can improve fracture simulator predictions and support the use of the fluid efficiency modifier. The liquid additive is easily implemented in the field. Wells treated with the polymer chemistry have better initial and long-term production, faster cleanup to gas sales, longer effective fracture length and require less pad volume while placing the same amount of proppant. The paper also describes high differential pressure leakoff test results at 7,000 psi to emphasize potential irreversible damage due to fracturing fluid invasion into rock matrix. This condition is more prevalent as treated reservoirs become deeper, especially in active tectonic areas around the globe. Tight gas wells with permeability from 0.01 to 0.14 mD show one year production improvements up to 41% due to the chemistry of the fracture efficiency modifier polymer included in the fluid. The wells typically were designed with reduced pad volume and production analysis suggests the wells show longer effective fracturing length, higher fluid efficiency and faster cleanup, while placing the same mass of proppant. Tighter wells with permeability of less than 0.005 mD showed higher conductivity with smaller fracture length. These wells showed cost reductions while yielding the same cumulative gas production.