Mobile Electronic Recording System and Drill-off Data Illustrating Its Use

Abstract

Abstract A mobile electronic system has been developed for recording drilling variables. Continuous records have been made, during field tests, of drilling rate, weight on bit, rotary rate, torque, fluid pressure and pump rate. Additionally, intermittent recordings have been made of strains and accelerations in various pieces of drilling-rig equipment, and longitudinal, torsional and bending stresses in the drill pipe. Transducers are placed on the rig for monitoring the variables. Cables connect the transducers through circuits to an oscillograph. The major electronic components of the equipment are housed in a trailer for protection and portability. The electronic recording system facilitates taking accurate drill-off data in the field. Data are presented on seven drill-offs taken in San Andres dolomite in Andrews County, Tex., at a depth of about 5,020 ft. In the test interval, drilling rate was proportional to weight on bit and to rotary rate raised to the 0.6 power. Introduction In the drilling research work conducted by Socony Mobil Oil Co., Inc., emphasis has been placed on a study of the factors affecting drilling rate, both with conventional and new drilling devices. The effects of several interrelated variables. have been studied. These include drilling rate, weight on bit, rotary rate, drill-string torque, drilling-fluid pressure and pump rate. In early field tests standard drilling-rig equipment was used in obtaining data. Because of the encouraging results obtained in these tests, an oscillographic recording system was fabricated. This mobile electronic recording equipment has been used successfully in the field and in the Socony Mobil Field Research Laboratory for four years. In addition to the mentioned variables, strains and accelerations in the drill string and in various rig components have been recorded and analyzed on several occasions. One such application occurred during Project Mohole, Phase I. Longitudinal, torsional and bending strains in the drill string were recorded while drilling in about 11,700 ft of water at the Guadalupe Island site. Several mechanical and electrical recording systems for drilling variables are now available for rental or purchase. These systems record from one to six variables. Accuracy, sensitivity, reliability and durability vary considerably on these units. The oscillographic system described in this paper was designed for improved accuracy and sensitivity. The subject recording equipment has many uses. One frequent application has been the obtaining of accurate drill-off data. In many instances the Lubinski calculation method for drill-off data is sufficiently accurate. However, in cases where severe buckling occurs during the drill-off or where the wall thickness of the drill pipe has changed due to wear or corrosion, this method can lead to considerable error. The technique described in this paper. utilizing the recording system, eliminates these inaccuracies. Description of the Recording System The mobile monitoring system is durable and versatile. It was designed for use in the field or in the laboratory. Signals from strain-gauge, potentiometric and tachometer-generator type transducers can be recorded. The frequency response and sensitivity of the circuits used for the various measurements can be varied over wide ranges. In fabricating the circuitry and components, simplicity was emphasized. This minimizes electronic problems resulting from transportation over rough terrain. Normally, signals are recorded without the use of amplifiers. During early field tests the apparatus was housed in a converted seismic-recording truck. The system was later installed in a house trailer. This instrument trailer is shown on the lower right in Fig. 1, together with the 1 1/2-ton truck used to transport the trailer. Hidden by the trailer is a portable 5-kw AC generator utilized for power. Fig. 2 is a block diagram of the transducers, recorder and control equipment. Each transducer is connected to the control circuitry by a shielded four-conductor cable. Fig. 3 shows the electronic equipment mounted in the trailer. The oscillograph recorder is located on the table at the left. The left relay rack contains an intercom system, control circuits for the transducers and a power supply. The right relay rack contains AC monitoring meters, a DC voltmeter, an oscilloscope and a voltage regulator. JPT P. 11^