Mitchell

Wellbore Stability and Wellbore Fluids

The two central topics for this issue of SPE Drilling & Completion journal are the two intimately related topics of wellbore stability and fluids used in the wellbore, either during drilling or for completion design and installation. Several papers directly address the topic of wellbore stability: a new, more comprehensive fracture model is proposed, methods for strengthening wellbores through propping fractures are studied, perforation plugging by produced formation particles is studied, and sand-control failure issues are discussed. Wellbore issues directly influence a number of fluid-design issues: a new cement is formulated to minimize formation hydrate decomposition, water-based muds are designed to prevent shale swelling, a comprehensive discussion of well-fluid choice in a major project is presented, and drill-in fluids to clean the formation are developed. Wellbore fluid even has an impact on tubing cutting.

If your interests focus on wellbore stability and fluid interaction, then this issue is for you. There are 14 papers in this issue. The following gives a brief overview of each paper.

Current State of the Premium Screen Industry: Buyer Beware, Methodical Testing and Qualification Shows You Don’t Always Get What You Paid For. Recent catastrophic sand-exclusion failures have led some operators and independent laboratories to perform additional testing and quality control checks. This paper describes a process to select sand-exclusion products by qualifying an individual product design, including retention media, metallurgy, subcomponents, manufacturing process, and the final assembled product. Cement-Slurry Design To Prevent Destabilization of Hydrates in Deepwater Environment. There is a compelling need to prevent destabilization of hydrates. The volume of cement results in a great amount of heat generated during setting, and the production of hydrocarbons increase the temperature of the formation. Cement slurries have been designed to lower the heat of hydration, and the improved cement-slurry designs lower considerably the thermal conductivity of the set cement sheath. Effect of Well Variables on the Performance of Chemical, Jet, and RCT Tubing Cutters  . An analysis of 72 tubing cuts in the Gulf of Mexico was completed to determine the effect of well variables on the cutting performance of chemical, jet, and radial cutting torch cutters. It was determined that chemical cutter success in CaBr₂ completions fluids was much lower than all other fluids combined, and that placing the pipe in tension significantly increased cutting performance. Designing Well Fluids for the Ormen Lange Gas Project, Right on the Edge. Because of environmental constraints and the selected sandface completion type, a water-based fluid system was required in developing the Ormen Lange field. The knowledge gained in the laboratory testing phase was transferred to the field. The first three wells of the initial development phase have been drilled and completed trouble-free, and the resulting production rates have met expected targets. Wellbore-Stability Performance of Water-Based Mud Additives. A critical property for many water-based muds is the ability to prevent near-wellbore pore pressure increase in shales, which promotes wellbore stability. All muds tested slowed the loss of overbalance pressure compared to a base-case brine fluid, but two muds were very effective at slowing and/or preventing the loss of overbalance. Measurements of fluid-induced swelling were also conducted in this same set of tests, and all four muds resulted in less swelling than the base-case brine. Correlating Flowing Time and Condition For Perforation Plugging By Suspended Particles. Accurate correlations were developed for the effect of pore throat to particle-size ratio on flowing fluid conditions and plugging time leading to particle bridging. Such empirical correlations can be used to determine and alleviate the conditions that induce perforation and pore plugging by migrating particles in petroleum reservoirs. Use of Ester as a Precursor to Clean Formate Drill-In Fluid Damage in Horizontal Wells. Formate-based brines have been used in drilling and completion operations for more than 10 years. Filter cakes that are generated by drilling fluids can act as a barrier to the fluid flow, and the conventional method for cleaning filter cake is by using solids-free formate brines. A new precursor ester generated an acid downhole at a low release rate, which results in uniform fluid distribution through the wellbore. This ester solution was more effective in cleaning the filter cake in comparison to the formate brines. Treatment of Hydrocarbon-Based Drilling Waste Using Supercritical Carbon Dioxide. Nonaqueous drilling fluids are essential in challenging drill operations, but they require special treatment and disposal because of their potential for environmental damage. In this paper, the results of a study using supercritical carbon dioxide to treat synthetic-based drilling waste are presented. Optimization of the process has yielded efficiencies as high as 97%. Further, the results suggest that the collected hydrocarbons may be reused in the drilling process, resulting in significant cost savings to the industry. Continuous Improvement in Slop-Mud Treatment Technology. Development of an understanding of the slop mud stream enabled a novel continuous treatment system to be built, which provides efficient and fast phase separation with recovery of the valuable drilling fluid phase, with significant advantages over current batch-type systems. Modeling Air and Water Perforator Swell for Better Risk Management. A detonated, shaped charge fired from a perforating string or perforating gun will not only perforate its targets but also possibly cause excessive damage or swell to its carrier. A method based on energy conservation is used to establish a swell model to predict the post-detonation conditions of the perforator, and a criterion is proposed to establish the serviceability of the perforators. Microwave Treatment of Oil-Contaminated Drill Cuttings at Pilot Scale. In the North Sea, there is a 1% residual oil limit for discharged cuttings. A thermo-mechanical cuttings cleaning process has produced cuttings with oil <1%, although with a significant deck-space impact and restricted throughput. Previous studies have shown that microwave treatment is able to reduce oil levels to well below 1% in a laboratory environment, and this work has studied the scaleup of the system to a 500 kg/hr continuous process. A Novel Technique for Determining Sand Screen Failure. Properly designed and executed sand-control completions are still subject to mechanical failure, with the first indications often being the production of solids into a common separation facility, where it is often difficult and expensive to determine which well or specific completion interval has failed. To solve this identification problem, a new proppant/gravel has been developed and tagged with over 20 unique markers that provide the ability to identify the exact well or zone that has failed. Investigation of Factors for Strengthening a Wellbore by Propping Fractures. Wellbore strengthening or stress cage implementation has been recognized as an effective means of dealing with lost circulation. However, a good understanding of this mechanism is necessary to avoid a potentially flawed design and implementation process that could adversely affect job success in the field. This paper describes those factors that are important in designing wellbore strengthening jobs and addresses the conditions necessary to ensure fracture stability. A New Fracture Model That Includes Load History, Temperature, and Poisson's Effects. A model for fracture initiation is presented, based on the classical Kirsch equation, but including the Poisson’s effects that arise when the borehole is pressurized from one stress state to another. As opposed to the classical Kirsch model, the new model starts with the initial in-situ stress and the virgin in-situ temperature. The mechanical and thermal loading towards fracturing is, therefore, modeled from this initial state.