Hydraulic Fracturing of CBM Wells in India Using a Unique Fracturing-Service Technology—Operational and Technological Lessons

Abstract

In 2009, a service company performed its first hydraulic fracturing treatment using a conventional hydraulic-fracturing technique in coalbed methane (CBM) wells in India. As progress was made, the potential for performing an extensive number of hydraulic-fracturing treatments in CBM wells was observed. From an operational standpoint, the advantages of recovering CBM wells are that they have more target coal seams at shallower depths that are candidates for stimulation, and the size of the treatments makes them ideal for multiple applications in a shorter period of time, reducing nonproductive time (NPT) for the operating company (Seldle and Arri 1990). The service company introduced a unique fracturing service that integrated two components—coiled-tubing (CT) deployed hydrajet perforating and then immediately performing hydraulic fracturing. By combining these two processes into one continuous service operation it eliminates the use of wireline for perforating and plug setting, making the new multistage technology economical for CBM wells. For the first time in India, this CT perforating/fracturing service was introduced to a CBM well operator. The observations and knowledge gained from the fracturing-service operations in India are discussed in this paper. This process employed hydrajetting technology through CT using a hydrajetting tool in the bottomhole assembly (BHA). Based on the casing specifications, cementing conditions, rock properties, and experience gained with each perforating experience, the jetting flow rates, differential pressures, and casing annulus backpressure requirements were optimized. This increased the life of the tool and improved the overall operations. The hydrajetting tool life was increased from 6 to 8 perforation sets to about 19 to 21 per tool, improving the operational efficiency. The advantages of jetting acid into the created perforations, pressure squeezing with acid, and using the many services of CT are examined. In addition, the BHA is also discussed. In some of the frac stages, the treatment screened out and experienced high concentrations of sand in the wellbore; therefore, the steps taken to help prevent sanding off the tool or getting the CT stuck are reviewed. Sand concentrations of 12 lbm/gal. were achieved for extended periods of time to pack the formations off. The need for using wellbore sand plugs was eliminated for many frac stages in these wells as a result of successfully packing the proppant into the fractures with higher sand concentrations. This helped eliminate concerns of losing fluid and sand into previous fractures when performing new frac stages uphole. As more treatments were executed and experience was gained, fluid usage was optimized and the fluid consumption was reduced by approximately 30 to 40%, providing further value to the operator. Finally, the lessons learned from a project- management viewpoint are also examined, discussing streamlining operations based on the various field and reservoir conditions experienced in India. The knowledge gained from this project could be directly applicable to the fracturing-service operations in other regions with CBM wells. The operational learnings during the course of this project could also serve as a guide to operations in this region where similar challenges are encountered.

The pilot appraisal of acid fracturing of coalbed methane reservoir in southeast Qinshui Basin, China

“…It was reported that small volume of acid spearhead ahead of the main fracturing had been implemented to clean out the cement deeper into near well bore area and reduce the breakdown pressure of a few CBM wells (Adil, Sharma, & Bhat, 2012). The acid spotting /socking with 1000 gal of inhibited 15% HCl and 10% Acetic acid mix, which react with perforation debris and remove cement invasion, has also been proved successful in India (Pooniwala, 2012).…”

“…To evaluate the feasibility of acid fracturing in QinShui Basin, herein a series of tests have been designed to verify that the acid is beneficial to dissolve the carbonate fillings in the coal core of both macroscale and microscale, and the pilot acid fracturing treatments have been performed to demonstrate that the HCl acid pad, the volume of which being much larger than that in literature (Adil et al, 2012;Pooniwala, 2012;Tamayo, Lee, & Taylor, 2007) can remove the carbonate cement of the natural fracture net, and lower the breakdown pressure efficiently as expected. It is learned from the microseismic survey that the stimulated reservoir volume (SRV) is dependent on the application of acid pad before the proppant laden stage, and it is suggested that larger volume of the acid pad is crucial to the success of the stimulation operation in CBM wells with carbonate filling in cleats.…”