High-Resolution Ultrasonic Borehole Imaging Enhances Reservoir Evaluation in Oil-Based Muds

Abstract

Obtaining high-resolution borehole images in oil-based mud (OBM) from logging-while-drilling (LWD) tools has been made possible through the recent development of ultrasonic imaging technologies. High-resolution acoustic impedance images enable reservoir evaluation through the identification of faults and fractures, bedding and laminations, and assessment of rock fabric. This paper presents examples of high-resolution images from a 4¾-in. ultrasonic imaging tool in OBM applications and discusses their value in assessing reservoir quality. This paper provides details of field trials of an LWD ultrasonic imaging tool for use in boreholes ranging from 5¾ to 6¾ in. High-resolution images detailing both borehole caliper and acoustic impedance in both vertical and horizontal wellbores are shown, illustrating the high level of formation evaluation now available when OBM is used. The methodology used to address the impact of tool motion on the impedance images will also be covered. The value of real-time data on borehole stability assessment will be discussed, along with additional applications made possible from the real-time data, such as wellbore placement enhancement. Both real-time and recorded data from field trials show the potential applications for the ultrasonic imaging tool. High-resolution impedance images covering different formations and lithologies show bedding planes and laminations and enable the calculation of stratigraphic dip, while the identification and assessment of fractures show the potential to aid operators during the development of their hydraulic fracturing program. Borehole caliper and shape assessment in real time can be used to modify the drilling parameters and to adjust mud weight, while providing an input into geomechanics assessment. The LWD logs presented illustrate the factors that influence data quality and the methodology used to ensure high-resolution images are available in both vertical and high-angle wellbores using OBM. A direct comparison between data acquired while drilling and while re-logging sections is shown, highlighting the repeatability of the measurement while also illustrating the impact of time-since-drilled on the borehole. A comparison with wireline measurements highlights the potential for using the high-resolution LWD images as an alternative to wireline, where cost and risk of deploying the wireline may be high. The ability to collect high-resolution images in OBM in wellbores ranging from 5¾ to 6¾ in. ensures that increased reservoir characterization is possible, leading to significant improvements in determining the viability of unconventional and other challenging reservoirs. The high-resolution amplitude images are comparable with those available on wireline technologies, and the real-time application of borehole size and shape for input into wellbore stability and geomechanics analysis ensures that common drilling hazards can be avoided.

Real-Time Method and Implementation of Head-Wave Extraction for Ultrasonic Imaging While Drilling

“…To improve the operation efficiency and reduce the extraction time, Equation ( 2) can be rewritten into Equation (6). In this way,…”

“…To improve the operation efficiency and reduce the extraction time, Equation ( 2) can be rewritten into Equation (6). In this way,N 2 L /N 2 S can be set as a constant, which is then directly stored into the register, and x(i) 2 and x(i − 1)•x(i + 1) can also be calculated in parallel.…”

“…This method uses ultrasonic transducers to detect wellbore media in a self-transmission and reception manner, and this logging can then accurately identify and measure the wellbore diameter, assess the shape and potential development of wellbore cavities and fractures in the open hole, and also evaluate casing damage and cementing quality in cased holes [1][2][3][4][5]. Wireline ultrasonic logging is relatively widely used, such as CAST, UBI, MUST, and MUIL [6,7].…”

Optimization of Pulsed-Wave Doppler Ultrasound for Estimation of Influx/Efflux in Oil and Gas Boreholes While Drilling Using Conventional Lwd Transducers

“…Ultrasonic LWD tools are routinely employed for obtaining high resolution images of the borehole wall with one of the important objectives directed at detecting the presence of fissures on the surface of the borehole wall. The imaging resolution of such fissures however is typically very low even for high-resolution LWD tools (Li et al, 2019), partly because of the hardware limitations in incorporating such tools with the BHA. These ultrasonic LWD tools typically map the amplitude and travel time of the echo from the borehole wall for imaging.…”

“…A high SNR of about 30 dB can be observed between the region with influx (the orifice) and the regions away from the influx. Conventional backwall-amplitude images as used in LWD tools (Li et al, 2019) were also generated from the same orifice plates as shown in Figs. 16(b) and 16(d).…”