Abstract: This paper illustrates how bit selection has been perfected by the research work on hard streak in Niger Delta oil fields. This enabled division of formation into soft (sand), hard (shale) and very hard (hard streak) away from former knowledge of only soft and hard. Borehole instability is pronounced while drilling in very hard formation or hard streak.This Formation is associated with siliceous-ferruginous sandstone with traces of siltstone rapped in augen of shale. Drilling through the tight streaks constituted a high risk to the drilling assembly with high axial vibrations (bit bounce) diameter and general rig operation. Placement of Mu– from the bit in the drilling string to drilling tools, mud, hole diameter, militating placement of Mud Motor on drill string for minimum speed. Also technical problems with old models – considerations only for soft (sand) and hard (shale) formation based on effective porosity between 5% and 20% by Skempton with disregard to less than 5% effective porosity of hard streak (hemaetitic matrix and cementation) became major driver to our solution. The regrouping of International Association of Drilling Companies (IADC) Bit Codes was a great enabler to division of rock formation into soft (sand), hard (shale or unconsolidated sandstone) and very hard (hard streak) thus making bit selection accurate. However, banking on experience, practical field documentations were made and data for this study were gathered through personal observation as a Directional Driller at Soku field. Others were from SPDC especially on Soku and Utorogu fields, NPDC’s Oredo field, DPR and series of research reading in internet. The data were subjected to analytical methods, presented in tables, figures and charts. Based on the data analysis and findings, it can be stated as follows:-
1. Sedimentary formation is hereby divided into soft, hard and very hard (hard streak) by this project models and suitable bits/drilling parameters delineated for each formation. Therefore,bits are selected with these models before and during drilling campaigns.
2. If drilling is on-going while any hole instability is encountered, you can as well query the Formation - the needed bit and drilling parameters are instantly produced for solution..
3. Insert bits aree very good for the hard streak, PDCs not good because of filing effects.
Concluding, the field experiences of the Soku, Utorogu and Oredo are worth been translated to other areas were the menace of hard streak or challenging formation is very common.
4. Comparable economics has shown that IADC code 447 bit costs only $196 to drill a foot than $120,000 of PDC, with a appreciable NPT savings of $1.2M within the hard streaks of about 5,000ft.
Keywords: International Association of Drilling Companies (IADC), hard streak, NPDC’s Oredo field, OPTIMAL BIT SELECTION.
Title: Analysis for Optimal Bit Selection: A Case Study of a Field in Niger Delta
Author: VICTOR U.K. OGUJIOFOR, ADEWALE DOSUNMU (PROF.)
International Journal of Thesis Projects and Dissertations (IJTPD)
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