Standoff and Caliper Measurements While Drilling Using a New Formation-Evaluation Tool with Three Ultrasonic Transducers
- J.R. Birchak (Halliburton Energy Services) | R.G. Matthews (Halliburton Energy Services) | G.L. Moake (Halliburton Energy Services) | W.E. Schultz (Halliburton Energy Services)
- Document ID
- Society of Petroleum Engineers
- SPE Drilling & Completion
- Publication Date
- June 1995
- Document Type
- Journal Paper
- 104 - 111
- 1995. Society of Petroleum Engineers
- 1.6.1 Drilling Operation Management, 4.1.2 Separation and Treating, 1.10 Drilling Equipment, 4.1.5 Processing Equipment, 1.5 Drill Bits, 3.3.2 Borehole Imaging and Wellbore Seismic, 1.11.2 Drilling Fluid Selection and Formulation (Chemistry, Properties), 4.6 Natural Gas, 1.14 Casing and Cementing, 1.6 Drilling Operations, 5.6.1 Open hole/cased hole log analysis, 1.10.1 Drill string components and drilling tools (tubulars, jars, subs, stabilisers, reamers, etc), 1.12.2 Logging While Drilling
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A new formation-evaluation LWD tool that employs three ultrasonic transducers to determine tool standoff and borehole diameter is presented. The ultrasonic data are used to improve density- and neutron-porosity measurements obtained from the same tool. The paper describes the ultrasonic transducer hardware and operating characteristics, as well as a unique technique for setting the ultrasonic threshold. Data processing procedures and caliper equations are also presented. Downhole phenomena that adversely affect the measurements are discussed, along with solutions used to handle them. Log examples illustrate the effectiveness of the ultrasonic measurements and include evidence of sticking, lateral bouncing, and whirling of the toolstring while drilling.
Measurements of borehole caliper and tool standoff are useful in drilling, cementing, and formation evaluation. Caliper information helps drillers detect borehole instabilities and estimate the amount of cement required to fill between the casing and formation. Also, information from a three-transducer tool may be used to inform the driller when the drillpipe is sticking or undergoing unusual motions in the borehole. Furthermore, caliper and standoff data are needed to correct density, neutron, and other formation measurements.
Despite the success of mechanical caliper devices in wireline logging, traditional designs will not survive the harsh conditions of drilling. In an effort to circumvent this problem, indirect methods are sometimes used to infer the borehole diameter from other logging-while-drilling (LWD) measurements. Recently, a more direct approach employing two ultrasonic transducers oriented 180 degrees apart was designed. Likewise, the LWD tool presented here uses a direct approach. The DNSC tool is a single module that makes density, neutron, standoff, and caliper measurements. Since it has three standoff transducers, more accurate caliper measurements are made than with a tool containing fewer transducers, particularly when the tool is sliding in the borehole. (We use the term sliding to refer to drilling with a mud motor, tripping into a well, or tripping out of a well.)
Although tool standoff information is used to improve the density and neutron computations, this paper concentrates on standoff and caliper measurements. The paper describes the tool configuration and operation, the response of the ultrasonic transducers, the standoff and caliper calculations, the accuracy of the measurements, and the data processing techniques employed. Ultrasonic data obtained while drilling during development and testing are presented to illustrate the ability to flag several conditions that are adverse to the drilling process, as well as to illustrate the accuracy of the measurements under these conditions.
|File Size||1 MB||Number of Pages||8|