Combining video and ultrasound increases downhole data capture accuracy

Downhole imaging technologies are proven tools for evaluating completions effectiveness. They achieve one component of this evaluation by comparing the entry hole sizes of perforations. As a perforation is abraded from proppant, the hole enlarges. Data measuring the magnitude of this erosion can be aggregated to provide more accurate insight into overall treatment distribution. Imaging technologies have helped operators optimize critical variables and identify the optimal perforation charge phase positions.  

TYPES OF IMAGING 

Until recently, two separate downhole imaging technologies have been deployed to evaluate perforation erosion: downhole video camera arrays that capture a 360-degree borehole view and multiple-transducer ultrasonic tools. Historically, the two have been considered separate methodologies, which means that operators only used one or the other to measure perforations. 

Proponents of each technology could cite the advantages of their chosen tool. Cameras have much higher resolution than ultrasound sensors and can measure perforation geometry with greater accuracy under suitable wellbore conditions. In fluids with low optical clarity, where cameras may not perform well, ultrasound sensors can provide measurements that capture general trends in proppant placement. Ultrasound arrays also can accurately measure inner pipe diameter and wall thickness, which can help detect and measure casing erosion, particularly at plug-setting depths.  

Each technology also has disadvantages. Camera lenses can become inoperative when they have been covered with opaque materials. In addition to delivering lower resolution than cameras, ultrasound can be susceptible to downhole motion effects, interfering with accurate measurement of perforations. 

COMBINATION IMAGING 

Rather than limiting downhole data capture to just one technology, research has shown that combining the two arrays captures more accurate and trustworthy data than either one could generate separately, Fig. 1.  For example, two recent field-tested wells offer insight into the benefits of the combined video-ultrasound tool string. Data for Well 1 was acquired for the 3,000 ft and 16 stages of the lateral section closest to the heel. For Well 2, the interval increased to 4,500 ft and 21 stages. 

Fig. 1. EVI results derived from ultrasound and camera measurements.

Benefits of combined strategy. Results demonstrate clear benefits of the combined tool string. If downhole conditions prevent one type of sensor from collecting usable data, the other can often fill in, allowing at or near 100% measurement of perforations. In Well 1, ultrasound sensors were able to measure 618 out of 663 perforations, while the camera array imaged all but one. In Well 2, the camera array was prevented from measuring 16% of the perforations, because its lenses became coated with an opaque material near the bottom of the logged interval. This material did not affect the ultrasound sensors, which missed only 3% of the perforations. As a result, the combined optical ultrasound arrays missed one perforation in Well 1 and six perforations in Well 2.  

Operators can now gain significant benefits through tandem use of the two technologies. EV ClearVision™ offers such a solution, combining 360-degree video and phased array ultrasound technologies. An integrated video and ultrasound scanning tool, it offers the most advanced 4D evaluation system for wellbore applications. ClearVision allows operators to see and measure 100% of perforations, including small-dimension perforations and those plugged with sand, Fig 2. Such complete and accurate data deliver trustworthy information related to perforation erosion and proppant placement trends. 

Fig. 2. Comparison of visual appearance and measured geometries.

CASE STUDY 

For a well in the Permian basin, the ClearVision tool string was deployed on coiled tubing, and data were acquired for the 3,000 ft and 16 stages of the lateral section closest to the heel. The well included some untreated base holes, providing in-situ dimensions used as a reference to calculate the eroded area of the treated perforations. 

Before implementing ClearVision, the operator used technology that resulted in 56% of the 16 stages missing perforations from two or more clusters, which invalidated the data for analysis purposes. In contrast, when the operator used ClearVision, 100% of the perforations were measured, delivering valid data for all stages to ensure accurate analysis. 

Such a high level of data completeness and precise perforation measurements allowed the calculation of proppant uniformity with complete trust in the integrity and validity of the acquired data. The operator identified the best-performing stage design and applied it to all stages of the next well, which improved reservoir stimulation. In its first year of production, the single well delivered additional production revenue of $1.4 million. Furthermore, the resulting increase in stage length and subsequent reduction in operating time yielded $350,000 in cost-savings and greater economic gain for the operator. 

Accurate data empower improved well performance. With the ability to deliver a high level of data completeness and precise perforation measurements, combined video and ultrasound arrays produce data at a previously unachievable level of validity and accuracy. Such trustworthy information is essential for making critical decisions with confidence and enabling improvements in the field that significantly impact the bottom line.