A series of field tests sponsored by Sandia National Laboratories has simultaneously demonstrated the hard-rock drilling performance of different industry-supplied drag bits as well as Sandia's new Diagnostics-While-Drilling (DWD) system, which features a novel downhole tool that monitors dynamic conditions in close proximity to the bit. Drilling with both conventional and advanced ("best effort") drag bits was conducted at the GTI Catoosa Test Facility (near Tulsa, OK) in a well-characterized lithologic column that features an extended hard-rock interval of Mississippi limestone above a layer of highly abrasive Misener sandstone and an underlying section of hard Arbuckle dolomite. Output from the DWD system was closely observed during drilling and was used to make real-time decisions for adjusting the drilling parameters. This paper summarizes penetration rate and damage results for the various drag bits, shows representative DWD display data, and illustrates the application of these data for optimizing drilling performance and avoiding trouble.
We have concluded a laboratory study to evaluate the survival potential of polymeric materials used for lost circulation plugs in geothermal wells. We learned early in the study that these materials were susceptible to hydrolysis. Through a systematic program in which many potential chemical combinations were evaluated, polymers were developed which tolerated hydrolysis for eight weeks at 500 F. The polymers also met material, handling, cost, and emplacement criteria. This screening process identified the most promising materials. A benefit of this work is that the components of the polymers developed can be mixed at the surface and pumped downhole through a single hose. Further strength testing is required to determine precisely the maximum temperature at which extrusion through fractures or voids causes failure of the lost circulation plug.
This report describes development of a system that provides high-speed, real-time downhole data while drilling. Background of the project, its benefits, major technical challenges, test planning, and test results are covered by relatively brief descriptions in the body of the report, with some topics presented in more detail in the attached appendices.
This proposal provides the rationale for an advanced system called Diagnostics-while-drilling (DWD) and describes its benefits, preliminary configuration, and essential characteristics. The central concept is a closed data circuit in which downhole sensors collect information and send it to the surface via a high-speed data link, where it is combined with surface measurements and processed through drilling advisory software. The driller then uses this information to adjust the drilling process, sending control signals back downhole with real-time knowledge of their effects on performance. The report presents background of related previous work, and defines a Program Plan for US Department of Energy (DOE), university, and industry cooperation.
Sandia National Laboratories is developing polyurethane foam as a chemical grout for lost circulation zones. In past work polyurethane foam was tried with limited success in laboratory tests and GDO sponsored field tests. Goals were that the foam expanded significantly and harden to a drillable firmness quickly. Since that earlier work there have been improvements in polyurethane chemistry and the causes of the failures of previous tests have been identified. Recent success in applying pure solution grouts (proper classification of polyurethane - Naudts) in boreholes encourages reevaluating its use to control lost circulation. These successes include conformance control in the oil patch (e.g. Ng) and dam remediation projects. In civil engineering, polyurethane is becoming the material of choice for sealing boreholes with large voids and high inflows, conditions associated with the worst lost circulation problems. Demonstration of a delivery mechanism is yet to be done in a geothermal borehole.
A high-speed data link that would provide dramatically faster communication from downhole instruments to the surface and back again has the potential to revolutionize deep drilling for geothermal resources through Diagnostics-While-Drilling (DWD). Many aspects of the drilling process would significantly improve if downhole and surface data were acquired and processed in real-time at the surface, and used to guide the drilling operation. Such a closed-loop, driller-in-the-loop DWD system, would complete the loop between information and control, and greatly improve the performance of drilling systems. The main focus of this program is to demonstrate the value of real-time data for improving drilling. While high-rate transfer of down-hole data to the surface has been accomplished before, insufficient emphasis has been placed on utilization of the data to tune the drilling process to demonstrate the true merit of the concept. Consequently, there has been a lack of incentive on the part of industry to develop a simple, low-cost, effective high-speed data link. Demonstration of the benefits of DWD based on a high-speed data link will convince the drilling industry and stimulate the flow of private resources into the development of an economical high-speed data link for geothermal drilling applications. Such a downhole communication system would then make possible the development of surface data acquisition and expert systems that would greatly enhance drilling operations. Further, it would foster the development of downhole equipment that could be controlled from the surface to improve hole trajectory and drilling performance. Real-time data that would benefit drilling performance include: bit accelerations for use in controlling bit bounce and improving rock penetration rates and bit life; downhole fluid pressures for use in the management of drilling hydraulics and improved diagnosis of lost circulation and gas kicks; hole trajectory for use in reducing directional drilling costs; and downhole weight-on-bit and drilling torque for diagnosing drill bit performance. In general, any measurement that could shed light on the downhole environment would give us a better understanding of the drilling process and reduce drilling costs.
Sandia National Laboratories and Tracor Applied Sciences have developed a proof-of-concept Expert System for the automatic detection and diagnosis of several important problems in geothermal drilling. The system is designed to detect loss of circulation, influx, loss of pump efficiency, and sensor problems. Data from flow sensors (including the rolling float meter), the pump stroke counter and other sensors are processed and examined for deviations from expected patterns. The deviations from expected patterns. The deviations are transformed into evidence for a Bayesian Network (a probabilistic reasoning tool), which estimates the probability of each fault. The results are displayed by a Graphical User Interface, which also allows the user to see data related to a specific fault. The prototype was tested on real data, and successfully detected and diagnosed faults.
One of the most common oil-field treatments is hot oiling to remove paraffin from wells. Even though the practice is common, the thermal effectiveness of the process is not commonly understood. In order for producers to easily understand the thermodynamics of hot oiling, a simple tool is needed for estimating downhole temperatures. Such a tool has been developed that was distributed as a compiled, public-domain-software spreadsheet. That spreadsheet has evolved into an interactive from on the World Wide Web and has been adapted into a Windows{trademark} program by Petrolite, St. Louis MO. The development of such a tools was facilitated by expressing downhole temperatures in terms of analytic formulas. Considerable algebraic work is required to develop such formulas. Also, the data describing hot oiling is customarily a mixture of practical units that must be converted to a consistent set of units. To facilitate the algebraic manipulations and to assure unit conversions are correct, during development parallel calculations were made using the spreadsheet and a symbolic mathematics program. Derivation of the formulas considered falling film flow in the annulus and started from the transient differential equations so that the effects of the heat capacity of the tubing and casing could be included. While this approach to developing a software product does not have the power and sophistication of a finite element or difference code, it produces a user friendly product that implements the equations solved with a minimum potential for bugs. This allows emphasis in development of the product to be placed on the physics.
Several wellbore hydraulic models have been examined to determine their applicability in measuring the characteristics of lost circulation zones encountered in geothermal drilling. Characteristics such as vertical location in the wellbore, fracture size, effective permeability, and formation pressure must be known in order to optimize treatment of such zones. The models that have been examined to date are a steady-state model, a standpipe-pressure model, a raising-the-drill-bit model, a mud-weight model, a hydrofracture model, and several time-dependent models. None of these models yet have been found to adequately match the field data obtained from six loss zones in three geothermal wells. The development of these models is presented in this paper, and a discussion of their limitations is provided.
One of the common oil-field wellbore problems is paraffin deposition. Even though hot oiling or hot watering is usually the first method tried for removing paraffin, few operators appreciate the limitations of ``hot oiling`` and the potential for the fluid to aggravate well problems and cause formation damage. Field tests have shown that the chemical and thermal processes that occur during ``hot oiling`` are very complex and that there are significant variations in practices among operators. Key issues include: (1) During a typical hot oiling job, a significant amount of the fluid injected into the well goes into the formation, and hence, particulates and chemicals in the fluid have the potential to damage the formation. (2) Hot oiling can vaporize oil in the tubing faster than the pump lifts oil. This interrupts paraffin removal from the well, and thus the wax is refined into harder deposits, goes deeper into the well, and can stick rods. These insights have been used to determine good ``hot oiling`` practices designed to maximize wax removal and minimize formation damage.