fax 01-972-952-9435.Abstract CO2 based fluids are commonly used to fracture stimulate formations with low reservoir pressure as well as formations that are more sensitive to water treatments (high capillary pressure, swelling clays etc). In particular, the Frontier Formation located in Bighorn Basin, Wyoming, has seen a variety of stimulation fluids used over the past years with varying degrees of success. When dealing with water sensitive formations, a common practice has been to use oilbased fluids. However, fluids of this nature can have detrimental effects on gas zones with low reservoir pressure and this might be the reason for erratic well performance of previously treated Frontier completions. It has also been determined that oil-based fluids can alter the reservoir wettability and hence cause formation damage. With this in mind and considering the environmental and economical benefits of using a water-based fracturing fluid, a novel viscoelastic surfactant based, CO2-compatible, high foam quality (>60%) fluid was proposed as the main fracturing fluid. This paper will discuss the first application of this visco-elastic based fluid on wells in Park County, Wyoming. This paper will discuss stimulation with the new fluid and how pin-point pressure measurement enabled the operator to make informed decisions to define fracturing/completion strategy. We also present the additional benefits of incorporating existing dipole sonic tool information to calibrate "in-situ" stress, Young's Modulus and Poisson's ratio. Finally, a production history match is conducted on wells treated with the new fluid.

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.

Friction reducers have been an integral part of the oil and gas industry for many years. They possess very unique properties of reducing friction pressure associated with the flow of fluid in tubulars. Friction pressure loss or hydraulic characteristics of friction reducers depend greatly on how they are tested and evaluated in the laboratory. Today, there is no standard procedure for their evaluation. American Petroleum Institute (API) oversees the development and publication of industry standard practices for various fluids and materials. Recognizing the need for a standard testing procedure for friction reducers, a Committee made up of members from industry and academia was formed and charged to develop a document outlining the standard procedure. Round-robin tests were conducted by four industry organizations and one academic institution, employing their in-house flow loops and were requested to report the results. Tests were to conduct friction pressure measurements of friction reducers, and to develop and deliver to the industry a standard procedure and method to measure and analyze friction reducers data in straight pipes. The test fluids chosen were two friction reducers: one anionic and the other cationic. Water data were also gathered as base line. Same fluid samples were submitted to all laboratories. The calibration procedure and fluid testing procedure was developed and distributed to all involved in fluid testing. The analysis for data reduction and for reporting results was also developed and distributed to all. It was found that the calibration procedure was more critical than originally thought. The determination of internal diameter of the circular tube is the most important parameter that influences the friction pressure loss results greatly. In this paper, the details of various flow loops, calibration procedure, data analysis procedure, and results obtained with water as base line and two friction reducers are presented and discussed. A standard procedure for testing and evaluating friction reducers for their friction loss properties is outlined. Following this standard procedure and carefully performing the testing with friction reducers will yield very similar results among various laboratories in the industry. This will make it easy when comparing the performance of friction reducers for their friction loss properties from different organizations.

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The field is located near the UAE capital, Abu Dhabi, with a tight oil and gas bearing carbonate formation. Rapid pressure drop observed, indicates slow charging from reservoir. Typically a tight reservoir like this is developed by hydraulic fracturing. However there is concern of fracture containment and placement. This study was conducted to construct a 3D reservoir geomechanical base model to optimize the completion strategy and production performances for the tight reservoir.176 laboratory tests/measurements on cores were performed to determine the mechanical properties and petro-physical properties at different intervals in 5 wells over the field. Eight 1D mechanical earth models (MEMs) were constructed to characterize the mechanical properties and stresses along the well trajectories, and the laboratory test results were used to calibrate the mechanical property profiles of the 1D MEMs. A 3D geomechanical model was constructed using seismically-interpreted horizons and faults; mechanical property population and boundary stresses were based on the 1D MEMs. Present-day stresses within the formation and surrounding formations were simulated, and stress evolution from 2011 to 2095 was predicted. Preliminary fracture modelling was performed at two wells to understand feasibility. The major concern is to control fracture containment within the reservoir section, particularly avoiding downward growth. The results indicate that there is tendency of fracture growth downward at one well. However, the downward fracture growth at the other well is not expected. The average upward stress barrier is around 400 psi over the field and the average downward stress barrier is around 800 psi. However, the magnitude varies from location to location. Five completion methods were compared in terms of geomechanics. Acid tunnel and fishbone completion have a very low risk in horizontal well stability. Multilaterals completion has a low risk in horizontal well stability and junction integrity. Acid fracturing and proppant has a relative high risk in fracture placement and containment. It is recommended to perform further completions feasibility study to review the feasible well location, productivity enhancement, economical aspect and operational constraints.This study reveals that the heterogeneity in the carbonate reservoir has a significant impact on the selection of completion methods. There is a high uncertainty to decide an optimal completion strategy based on 1D geomechanical study results because the large variations in the in-situ stress and mechanical properties. Therefore, a 3D geomecanical study is necessary for the completion selection for heterogeneous carbonate reservoirs, particularly for tight thin plays.