[01] Onuorah Joshua Nwani, Department of Petroleum Engineering, Faculty of Engineering, University of Benin, Benin City, Nigeria.

In order to achieve the purpose of improving the understanding of drilling bits performance at a particular depth in the Niger Delta region of Nigeria, a simple performance optimization model – ‘Matching the Area Average Performance’ was used to ascertain the actual performances of selected drilling bits used in the region against their prevailing drilling variables in terms cost evaluation. In this model, Cost per Foot equation was used to compare the performances of the selected drilling bits on the basis of minimum Cost Drilling for two case study wells - Agbada 1 and Soku 56, located in the heart of the region with depth range of 3,000 feet to 20,000 feet respectively. The interpretation of graphs of the relationships between Depth, Cost per Foot and Total Run Cost of a particular drilling bit size gave a proper downhole drilling analysis of two the two wells in the region hence, illuminating the behavior of a drilling bit at a particular depth amidst the prevailing drilling variables in the region. The selected drilling bit sizes were 17½, 12¼ and 8½ inches of predominantly PDC bit types representing surface, intermediate and production casing stages respectively. The prevalent formation/lithology of the region is Agbada formation. The evaluated drilling variables include the Rotational Hours, Rate of Penetration (ROP), and Weight on Bit (WOB). The effect of these important variables was used to determine the Cost per Foot Drilled and Total Run Cost (TRC) for the two Wells. The result obtained from the work was recorded and presented as an organized graphical analysis of the cost performance record of the selected bits used for the two wells. This is believed to be an invaluable tool that will enable stakeholders in the drilling business to make an informed and economically viable decision on the selection of a drilling bit run conditions and the drilling system design that will minimize economic downtime when drilling a new well in the region.

Drilling Optimization, Polycrystalline Diamond Compact (PDC) Bit, Cost Per Foot, Rotational Hours, Drilling Variables/Parameters

[01] Ejadawe, J. E., Coker S. J. L., Lambeth, Aikhionabare, O. O, Alofe, K. B., and Adoh, K. B., (1984). Evolution of oil-generative window and oil and gas occurrence in tertiary Niger Delta Basin AAPG Bulletin 68, 1744-1751. [02] Avbovbo, AA (1987). Tertiary Lithostratigraphy of the Niger Delta. A. A. P. G Bull. 162. P 295-300. [03] Doutst, H., and Omatsola, E., (1990). Niger Delta in, Edwards J. D., and Santogrossi, P. A., eds., Divergent/passive margin basin, AAPG Memoir 48: Tulsa: AAPG, pp 239-248. [04] Reijers, T. J. A., Petters, S. W. and Nwajide, C. S., (1997). The Niger Delta Basin [In:]. [05] Nwani O. J (2012) Review of the Performance of Selected Drilling Bits Used in the Niger Delta Region of Nigeria. [06] Holster, J. L. and Kipp, R. J. (1984). Effect of bit hydraulic horsepower on the drilling rate of a polycrystalline diamond compact bit, SPE 11949, Annual Technical Conference and Exhibition, San Francisco, October 5-8. [07] Ambrose, D. (1987). Diamond cone bit performance analysis. Unpublished Ph.D. thesis, University of Nottingham. [08] Shah, S. M. A. (1992). The optimization of PDC bit performance in coal measures rocks. Unpublished Ph.D. thesis. University of Nottingham. [09] Gray G. R., And Young Jr., F. S. (1973). 25 Years of drilling technology: A review of significant accomplishments. Journal of Petroleum Technology, December, pp. 1347-1354. [10] Bourgoyne, A. T. Jr., Millheim, K. K., Cheneverert, M. E. and Young, F. S. Jr. (1986). Applied drilling engineering, Society of Petroleum Engineers, Richardson, TX, 502p. [11] Hariot–Watt University Drilling Engineering Textbook. [12] Ward Law, H. W. R. Optimization of Rotary drilling parameters PhD Dissertation, University of Texas. August 1981. [13] Adams and Rountree CSTSUM Technology Program. [14] Annajul Rosari Nigeria Limited (2011). Drilling bits document.