Abstract

A critical cost in future deep oil and gas recovery is the cost to drill a well. This cost is dominated by the rate of penetration (ROP) that becomes increasingly important with increasing depth. Improving the technology of drilling and increasing the ROP will lower the cost to drill a well. This improves the economics of deep exploration and development, potentially increasing drilling activity, increasing production and supply, lowering the cost to the consumer and improving the economy.

Industry partners and the U.S. Department of Energy (DOE) successfully completed benchmark testing of advanced diamond bits and high pressure/high temperature (HP/HT) drilling fluids at high pressures. The paper describes the results of this testing and identifies factors limiting ROP performance at great depth, and the development of drilling fluid systems and bit design philosophy to significantly improve drilling performance. Benchmark results match very well with data from target field applications. This project is part of the DOE Deep Trek program.

Sixteen full-scale tests of 6 inch bits were conducted at wellbore pressures greater than 10,000 psi. Results from high pressure tests with water and base oil showed very high ROPs are possible before mudding up. When drilling through hard sandstone penetration rates can drop 70 to 80% on switching to a weighted mud. These data emphasize the importance of mud technology in high-pressure applications. Performance of polycrystalline diamond compact (PDC) bits showed in many cases substantial improvements over roller cone insert bits.

Cuttings from Carthage marble and Mancos shale appear to be compressed agglomerates of fine particles and Carthage marble cuttings had low compressive strengths. The study has concluded that opportunities for improvements in both bit design and smart HP/HT drilling fluids are possible. While rock properties change continuously with pressure the cutting mechanisms at great depths change much more dramatically. Changes in bit design and mud composition, using next generation technology, will be evaluated in Phase II testing.

The significance of improved ROP for deep oil and gas plays include opportunities to reduce well costs and improve the economics of deep exploration and development plays. The net result for operators is cost reduction as well as an improved position on reserves.

Summary

Full-scale laboratory testing was conducted under a joint industry and Department of Energy program titled "Optimization of Deep Drilling Performance; Development and Benchmark Testing of Advanced Diamond Product Drill Bits and HP/HT Fluids to Significantly Improve Rates of Penetration." Simulations of deep well drilling in the Arbuckle play and the Tuscaloosa trend was accomplished during full-scale, high pressure tests using four different drill bits, three types of rock, and five different drilling fluids.

This paper describes what is believed to be the first set of full scale laboratory drilling tests yet performed at bottomhole pressures in excess of 10,000 psi. Accomplishments of the testing and analysis included:

  • Laboratory testing provided a reasonable simulation of field drilling conditions encountered when penetrating hard rock at high bottomhole pressures. This was confirmed by comparing field data with laboratory results of tests at conditions similar to those in the field.

  • "Mudding up" at high bottomhole pressure causes penetration rate reductions anywhere in the range of 30 to 80%.

  • Testing showed that polycrystalline diamond compact (PDC) bits have substantially higher penetration rate potential than do impregnated and roller cone bits, even when allowing for the lower operating weights typical of PDC bits. Impregnated and roller cone bits are typically 60 to 80% slower than PDC bits at equivalent weights on bit in the environments investigated in these studies.

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