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ONGC opened the well through a 40⁄64-in. choke but gradually reduced the choke to 16⁄64-in. because of sand indications at surface.
Flow back continued through a 16⁄64-in. choke. During flow back, the well flowed water along with a little gas. Thus, ONGC decided to produce the remaining water with artificial lift and testing of RNSG 1 No. 1 was suspended temporarily.
A temperature log recorded 7 days after the third frac indicated a considerable temperature drop (about 40° F. at the first perforation) across all the hydraulically fractured zones. A gradient plot suggested water inside the 95⁄8-in. by 51⁄2-in. annulus.
No gas was seen while bleeding off the annulus and casing pressure. During the bleed off, the pressure dropped to zero in a couple of minutes with a little muddy water recovered.
During flow back, gas surfaced within 3 hr of the first frac job. In the case of the offset coalbed methane well (Fig. 2), it required many days of dewatering before gas broke through after a frac job.
The shale-gas well had poor cement because of a micro annulus behind the 51⁄2-in. casing. Cement quality behind the 95⁄8-in. casing (shoe at 879 m) is not known because no cement bond log or variable density log was run.
The suspected reason for losing total returns at about 500 m is the intersection of a major fault zone with the wellbore.
At temporary abandonment of the well, both the casing and annulus pressure was 400 psi. The pressure started dropping gradually and coincided with the resumption of dewatering of the offset coalbed methane well.
Casing pressure bled off to zero on Mar. 23, 2010, and since then has increased and stabilized at 50 psi. Annulus pressure was not bled off and currently is about 150 psi.
Water influx from the offset coalbed methane well is an explanation for the buildup of the annulus and casing pressures.
Issues
One challenge in operating in India is security. In India, security personnel must guard every drill site to prevent the local population or others from stealing instruments and tools for resale.
Other problems in developing a field are the lack of skilled engineers (most prefer to go abroad), proper care and knowledge of the field, population density, and politics. One saying is that "Shale can bring riches and energy independence, but development creates a continuous series of tough decisions on how to balance public benefits against the costs to the same public."
Reliance Industries Ltd. and Gail India Ltd. are starting to exploit and acquire overseas assets in shale gas. This should help these companies also to explore for shale in India because of the technical and business knowledge gained overseas.
Companies operating in India initially have to import most oil field goods, which leads to higher cost.
Costs of oil field services also are higher because of the limited competition, and lack of clarity in regulations may limit the number of oil field service companies participating in India's shale-gas exploitation.
An estimate is that India's companies will need a 5-10 year learning curve to develop excellence in executing such technologies as horizontal drilling and fracturing as well as implementing a factory approach to shale-gas development that would bring down costs.
Although not all shale deposits in India are ideal for shale-gas exploitation, a substantial portion has potential for producing gas. Technological collaboration will help in the use of sophisticated models to select the most prospective places to drill.
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