Prof Dosunmu Adewale 's research grant

Lead Researcher

Title Prof
Firstname Adewale
Surname Dosunmu
Phone 08033124495

Research Grant Details

Research Topic Data base for Wellbore Stability Management in the Niger Delta
Benefit to Oil and Gas Software developed for use in Well Bore stability study has useful application in regional and global analysis. Optimization study of Well Spacing and Management in the Niger Delta. Job creation and high revenue windows.
Research Duration 2
University University of Port Harcourt
Abstract Wellbore instability in shale formation poses a serious challenge to the oil and gas industry worldwide during and after drilling. Drilling and completion operations continues to be plagued by various hole problems directly attributed to the instability of shale formations. This has resulted to an enormous yearly expenditure for the drilling industry. It is estimated that wellbore instability problem costs the oil industry economic losses to the tune of about 1 billion US dollars each year (Chenevert, 2002, Zeynali, 2012); the lost time due to this challenge also account for over 40% of all drilling related non-productive time (Zhang et al, 2009) and these instabilities are responsible for 10-20% of the total drilling cost. A solution through this challenge is critical to the sustenance of the investment made by companies in the oil and gas industry. A comprehensive solution will drastically reduce drilling cost, completion and workover cost as well as the accompanying downtime involved. Shales have been generally defined as low-permeability sedimentary rocks with small pore radii that are characterized by low permeability, medium to high clay content, and medium porosity (Zhang, 2005), in addition to other minerals, such as quartz, feldspar, and calcite (Osisanya, 1991). According to Manohar (1999), the distinguishing features of shale are its clay content and low permeability, which results in poor connectivity through narrow pore throats (pore throat diameters are within the range of 3nm to 10nm). Shales are also fairly porous and are normally saturated with formation water, with several factors affecting their properties, such as burial depth, water activity, and the amount and type of minerals present in them (Joel, et al. 2012). These characteristics make them susceptible to different phenomena including swelling, shrinkage, hydration and mechanical failure. Dzialowski et al (1993), submitted that 75% of the formation drilled the world over are classed as shale formation and about 90% of drilling operations problems are related to shales, hence most wellbore stability researches are concentrated on shale formations. Researches have been conducted to study the effects of several factors related to the stability of the wellbore in relation to shale. These include phenomena such as osmotic effect, cation exchange capacity, mineralogical content, hydration tendency, shale strength etc. Osisanya (2012) submitted that “wellbore instability is recognized when the hole diameter is markedly different from the bit size and the hole does not maintain structural integrity, hence under gauged or over gauged holes”. Some indicators of wellbore instability are shown in Table 1.1.This instability can be caused by a combination of both controllable and uncontrollable factors (natural and human). It is believed that the main cause of shale instability stems from unfavorable interactions between the drilling muds and shale formations (Chenevert, 1970; Bol, 1992; Van Oort, 2003). Perez, (2002) posited that “wellbore instability problems are generated from rock variation during the drilling process as a consequence of the stress experienced due to their varied and complex mineral composition, as well as the composition of the drilling fluids utilized in the operation (variations are caused not only by physical but also by chemical media)”. The factors causing wellbore instability were grouped under three interrelated headings, namely mechanical, rock-chemical interaction (shale) and man-made (drilling practices) by Osisanya (2012), as shown in Fig. 1.1. Understanding the complexity of these causes is critical to the maintenance and control of wellbore stability. When a well is drilled, the formation around the wellbore is expected to sustain the load that the removed formation previously carried. As expected, there will be a resultant increase in stress concentration and the stress around the wellbore. If the formation is not strong enough to sustain the increased stresses around the wellbore, the wellbore will fail. This failure can also be attributed pore pressure changes and mechanical property alterations around the wellbore. Such wellbore instability is said to be due to geo-mechanical effects of drilling a well into the formation. According to AL-Bazali (2005), “mechanical failure takes place when the stress acting on the wellbore exceeds the shale strength. This phenomena occurs when the mud weight is either too low (compressive failure) or too high (tensile failure)”. Chemical wellbore instability is related to shale formations and their physio-chemical interaction with drilling mud and pore fluids. Unlike mechanical wellbore instability that has been extensively studied and modeled in the Niger Delta, chemical instability in the region has been poorly investigated and incompletely understood. The flow of water and ions in and out of shale has been attributed to be the primary reason for chemical wellbore instability of shale. The traditional idea that the reaction of shale with drilling fluid usually reduced the strength of the shale fits well with field observation (Santos, 1997). Effective management of wellbore instability requires knowledge of both regional and field characteristics of the formation so that fit-for-purpose technology can be deployed and applied. Therefore understanding shale-fluid interaction and other basic concepts of shale as well as studying the properties of shale, its mineralogy and how these properties are affected by changes in the composition of our drilling fluids are imperative in surmounting most shale related wellbore stability problems.

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