TX 75083-3836, U.S.A., fax 1.972.952.9435. AbstractThe paper is an update to the current status of laser drilling technique -the first fundamental change to rotary drilling. We begin with a brief note on history of physical tests in 60's and 70's which were limited by the laser technology and low power available at that time. Seven lasers have been identified for potential use in the upstream oil industry. Each rock type has a set of optimal laser parameters to minimize specific energy as observed in the linear track tests. Current efforts are focused on underwater laser drilling.Next, stress has been put on the basic scientific principles that can bring laser drilling within reach of an industry-supported prototype. Hence, the methods of delivering laser radiation and rock removal from wells drilled followed by parameters like feasibility, economics, benefits and environmental impact related to laser drilling have been discussed.Laser drilling is found to be more efficient, cleaner way to drill and perforate wells through hard rock formations encountered at greater depths. The effects of the laser rock interaction on permeability have also been studied. Laser perforation resulted in permeability improvements. One of the major advantages of laser drilling is its potential to reduce drilling time. Lasers cut drilling time by not contacting the rock, eliminating the need to stop and replace a mechanical bit. Finally, we end with a discussion on the wider scope of laser technology for on-site tasks including cutting windows for side exiting casing or laterals, extended perforations that connect additional reservoir rock to the well bore, and removal of objects lost down hole that would normally require drill out or fishing operations.

This paper presents a more holistic approach to compare the drilling economics of Synthetic Oil Based Mud (SOBM or SBM) versus Water Based Mud (WBM) in onshore development drilling in India. Here, a key parameter which has been incorporated in the economics is the mud re-use and overall consumption trend of SBM versus WBM, which has been analyzed from statistical data across 200+ wells and quantified into overall cost savings with SBM estimated across roughly 500 development wells drilled. The surface holes in all the development wells were drilled with WBM instead of SBM to avoid contamination of shallow water aquifers. Hence, the performance evaluation of SBM was limited to intermediate and production holes only, which were drilled with SBM. Also, past exploration and appraisal wells had used WBM for drilling these hole sections. A key parameter calculated from statistical data was average mud consumption (barrels per meter drilled) for SBM and WBM. The mud consumption of SBM and WBM is expected to differ because theoretically SBM can be re-used across greater number of wells compared to WBM. The average mud consumption was separately calculated for different hole sizes to better analyze the effect of hole size on mud consumption. The actual cost incurred with SBM application in development wells was calculated. Next, cost for drilling these wells with WBM was estimated using mud consumption (barrel per meter) data obtained from exploration/development wells. These two cost scenarios were compared to arrive at the net cost savings with SBM compared to WBM. A maximum cost savings upto ~10 MMUSD (for various sensitivities especially SBM cost per barrel) is estimated across 500 wells in spite of the higher contracted costs of SBM (cost per barrel) when compared to WBM. The maximum cost saving of ~10 MMUSD corresponds to anticipated reduction in base oil cost in the current crude market. The savings with SBM are mainly attributed to the fact that SBM can be theoretically re-used infinitely moving from one well to the other while the WBM can be re-used for a limited number of wells. This cost model excludes any savings on part of SBM due to improved hole conditions and resultant reduction in drilling non-productive time. SBM system minimizes drilling problems due to good clay inhibition, enhanced hole cleaning, lubricity additionally SBM is least effected by contamination. However, the higher cost per barrel of SBM and associated environmental concerns normally act as deterrents for operators to choose SBM for planning their wells. This paper provides clarity on the perception "SBM is costlier to WBM" and reinforces the recommendation to use SBM for drilling operations from an overall cost perspective.

Drilling horizontal wells at an average true vertical depth (TVDBRT) of 850-950m to exploit the high porosity and low permeability tight reservoir of Barmer Hill (BH 1 to BH12), in the Indian state of Rajasthan required overcoming many chal-lenges. These wells were drilled from both Aishwariya and Mangala fields. The highly layered BH reservoir is primarily composed of diatomite and porcellanite. Drilling ERD wells at such shallow depths and with land rigs that have limited capability (tubular and pump limitations) required detailed planning and flawless execution because of many inherent risks such as high torque and stand pipe pressures, poor hole cleaning, inadequate weight-on-bit transfer and stuck pipe events. Optimum trajectory in terms of good well placement, drillability and collision risk avoidance was a priority in planning these wells in a tight network of over 350 wells. An important concern was designing a Bottom Hole Assembly (BHA) to meet multiple requirements. It had to be planned to maximize achievable doglegs with Rotary Steerable System (RSS) to land the wells despite high uncertainty in reservoir depths.High drilling torque anticipated in 6″ hole and narrow operating window with re-spect to helical buckling were major concerns.WOB transfer while drilling ~1000 m horizontal section was critical. ECD had to be carefully managed by a combination of good hole cleaning and the use of smaller drill pipe in order not to exceed formation fracture gradient. Good drilling practices specific to ERD wells and meticulous engineering/planning led to successful drilling of these shallow TVD ERD wells.

This paper explains the successful execution of Expandable Liner Hanger and primary cementing job for ERD wells in Rajasthan block of North-West India. One of these wells has the longest horizontal 6in. hole section in the Indian Subcontinent. Zonal isolation is especially critical, as these wells are all candidates for multistage fracturing operations in the completion phase. The successful liner job in these wells face several challenges: placement of 4½ inch liner in 6 inch hole, hole conditioning, cement placement and ECD challenges due to low fracture gradient limit. An integrated Basis of Design was developed to mitigate the challenges. This includes The placement of liners with computer aided torque & drag analysis,Rotation of liner during hole conditioning & cementing at highest possible rpm within acceptable torque limits,Fine tune fluid properties with computer aided simulator to achieve sufficient cement coverage around the liner (displacement efficiency). The liner hanger system in this case study has an advanced running tool to facilitate the required rotating capability. The liner hanger also incorporates a contingency tertiary setting mechanism for liner expansion due to the challenging down hole condition. The expandable liner hanger is an integrated hanger packer system. Elastomeric elements are bonded on to the hanger body itself. As the hanger body is expanded, the elastomeric elements are compressed in the annular space, which provides primary annular isolation at liner top. This case study also examined the impact of liner rotation on displacement efficiency of the cement slurry with computer aided Finite Element Analysis. The results give engineers a better understanding of the relationship between rpm and displacement efficiency of the cement slurry. The technology and the practices established from this case study have become the standard operating procedures for liner cementing jobs in subsequent ERD wells.

On January 19, 1975 an earthquake of magnitude 6.8 occurred in the border districts of Himachal Pradesh, India. The earthquake caused considerable loss of life and varying degrees of damage to construction in the area. Traditional and recent buildings suffered extensive damage. Landslides, rock falls and avalanches caused considerable damage to the Hindustan-Tibet road. Extensive fissures in the ground developed at the epicenter. Greatest damage was noted along the N-S trending Kaurik-Chango fault following the Parachu and Spiti river valleys, suggesting its genetic interrelationship with the earthquake.