Use of a Downhole Mud Motor as a Pump for Drillstem Testing

Abstract

Summary The increasing expense and complexity of exploration drilling, coupled with rapid advances in computer and microprocessor technology, have led to the development of computer-assisted wellsite logging units. This paper discusses two methods currently in use for the collection and storage of rig and mud data during drilling and tripping operations and application of these methods to improve wellsite safety and drilling efficiency. Introduction Mud logging units first were employed in the search for hydrocarbons in the early 1940's. In the following decade, advances in gas chromatography and electromechanical sensors enabled these same units to measure combustible gases and rate of penetration more accurately. In the latter half of the 1960's, an increase in the number of exploration wells being drilled in more dangerous offshore locations and geologically unpredictable environments, such as the North Sea, led to a growing awareness of the need to improve fig safety and to reduce spiraling drilling costs (Fig. 1). As a result of this need, the monitoring and recording of an ever-increasing number of drilling parameters has become the norm. Development In the interests of safety and, in particular, in an attempt to reduce the incidence of loss of life and/or property resulting from blowouts, empirical methods were developed in the mid-1960's to identify abnormal pressure regimes with some of the many drilling parameters recorded. Jorden and Shirley (with later refinement by Rehm and McClendon), for example, developed for the Gulf of Mexico the drilling or d exponent to normalize the effects of weight-on-bit (WOB), rotary speed, and bit size on drill rate and to try to make the d exponent accurately reflect changes in pore pressure. The requirement for instantaneous and accurate measurement of these parameters was extremely important. Furthermore, changes in flow-out, mud weight, and pit level remained important factors in preventing a kick from becoming a blowout. Hence the accurate measurement of the drilling and mud parameters was crucial. Drill monitoring systems included kelly height, fig heave, hook load, WOB, rotary speed and torque, and casing and standpipe pressure. Mud monitoring systems included mud weight, temperature, resistivity, and flow in and out, pump strokes, total pit volume, and trip tank volume. Gas monitoring systems included chromatographic analysis and detection of hydrocarbons, H2S gas, CO2, nitrogen, and oxygen. Centralization of Data Recordings One serious drawback was that readings were taken at many different locations on the fig. Mud weight was measured in the pits and on the shakers, the driller's weight indicator displayed WOB, and the geolograph recorded standpipe pressure, torque, rotary speed, and hook load. A separate instrument was used to show changes in pit level. JPT P. 2899^