Mitchell

Back to the Future

The history of "scientific" oil-well drilling has its beginnings at the end of World War II. The first wave of scientific drilling was an era of slide rules and hand calculations. The technology of this era consisted of relatively simple, but effective, models of very complex phenomena. Claude Hocott once told your editor that any calculation that could not be summarized on a note card would not be useful, and for that era, he was correct. Today, it is hard to appreciate the tedium of evaluating these simple formulas with slide rule, tables of logs, and pencil and paper.

The next wave of scientific drilling introduced a new computational tool, the electronic computer, beginning in the 1970s. Young engineers, who had used primitive computers as part of their university education, were now ready to break Hocott’s one-card rule and delve into the complexity of the phenomena of drilling.

Your editor speculates that we are beginning a third wave of scientific drilling. The days of novel computer application are reaching their twilight years, and a period of evaluation and consolidation is beginning. Computer science and numerical analysis are at a much higher level of accuracy and sophistication today than they were in the 1970s era, and many of the technology developments of that era should be re-examined in the light of modern techniques.

In this issue, there are four completion topics and nine drilling topics. The completion papers consist of the following papers: A New Skin-Factor Model for Perforated Horizontal Wells answers the question: "What is the best way to perforate horizontal wells with anisotropic permeability?" The results show that the azimuth of the perforation is the key. If the perforations are normal to the maximum permeability direction, perforations will enhance horizontal well flow compared to an open hole completion. Geomechanics Aspects of Multiple Fracturing of Horizontal and Vertical Wells. Although fundamentally similar to fracturing vertical wells, fracturing horizontal wells have unique aspects that require special attention for successful treatment. Because fracture orientation depends on well direction relative to the formation stresses, successful fractures depend on the well completion and its orientation, which is further complicated by the presence of multiple fractures. An Alternative to Sand-Control Screens: Is Permeable Cement a Viable Option? First, the bad news: for a variety of reasons detailed in this paper, permeable cement does not yet appear to be a viable option as an alternate sand-control method for primary openhole completions. However, the system presented in this paper may find use in remedial sand-control situations. For instance, squeezing perforations with permeable cement could ensure sand-free production over a limited time while maintaining full wellbore access. Design and Implementation of Retention/Filtration Media for Sand Control. The factors that control the performance of sand-control screens that use different metal mesh weaves is not generally well understood. This paper provides techniques to design and engineer a premium sand-control screen with retention/filtration for the specific particle size distribution of the formation, maximizing oil production while minimizing solids production.

The drilling papers include: Remote Real-Time Well Monitoring and Model Updating Help Optimize Drilling Performance and Reduce Casing Strings. Feedback and updating the pre-drill velocity-to-pore pressure with real measured data enabled accurate pore pressure prediction in a GoM well. The monitoring of true formation pressure thus allowed drilling to proceed within the constraints of a very tight mud envelope, resulting in a deeper casing seat and elimination of an entire casing section. State-of-the-Art in Coalbed Methane Drilling Fluids. For horizontal coalbed methane wells, the importance of the drilling fluid is magnified because the fluid must stabilize the wellbore during drilling but minimize damage to production. In this paper, the fluid is designed to match surface chemistry of the coal, and provide both a matting system to provide borehole stability and a breaker method to remove the matting once drilling is completed. Transport of Small Cuttings in Extended-Reach Drilling. Field experience has shown that inefficient transport of small cuttings is a main factor for excessive drag and torque during extended reach drilling. Drillpipe rotation combined with polymeric drilling fluids was found to efficiently transport small cuttings during extended reach or horizontal drilling. Hole Cleaning During UBD in Horizontal and Inclined Wellbore. This paper presents a new mechanistic model for cuttings transport, developed by combining two-phase hydraulic equations, turbulent boundary layer theory, and particle transport mechanisms. It is shown that the model is useful for predicting minimum annular velocity and cuttings bed thickness in horizontal and inclined wellbore geometry. Kikeh Batch Setting: Case Study. The semisubmersible rig Ocean Rover was used by Murphy Sabah Oil Company to batch-set 23 wellheads in 4,350-ft-deep water with zero health, safety, and environment (HSE) incidents. Implementing lessons learned and development of recommended practices resulted in continuous improvement throughout the project. Improving Formation-Strength Tests and Their Interpretation. Crucial decisions on mud weight, kick tolerance, and the setting depth of the next casing string are based on the outcome of formation-strength tests such as leakoff tests or formation-integrity tests. In this paper, the authors highlight several of the problems underlying current formation strength tests and their interpretations, illustrating them with actual field examples, and they show how test artifacts can be either avoided or accounted for. Design of Well Barriers to Combat Circulation Losses. This paper presents a new mechanistic model for fracturing called "the elastoplastic-barrier model." It is different from other recent models, and it is verified with laboratory experiments. It defines optimal barrier filtrate loss to place particles in the loss zone, and the mechanical strength of the particles required to resist losses. Tests demonstrated that borehole fracturing resistance could be improved significantly by changing mud composition. Shear-Type Borehole Wall Shifts Induced During Lost Circulations. Previously, stuck pipe problems were assumed to be caused by borehole breakouts, differential sticking, and cutting pack offs. However, thorough examinations of borehole walls using borehole televiewers show that some stuck-pipe problems may also be caused by shear type borehole wall shifts. In this paper, a new fracture model for a borehole is developed using a 3D-dual-boundary element method. This method allows different displacement and stress traction at the two fracture surfaces along a fracture plane around a borehole. A New Method of Producing Laterally Stable PDC Drill Bits. Bit whirl is well documented as a major cause of damage to polycrystalline-diamond-compacts (PDC) drill bits, and result in short runs, low rate of penetration (ROP), high cost per foot, poor hole quality, and downhole tool damage. Hence, consistent lateral stability is highly desirable in PDC bits. The paper presents a new method of producing PDC drill bits that reduce or eliminate bit whirl. The new approach assumes that it is the response of the bit to forced motion off its center that causes whirl.