Design and evaluation of wellbore strengthening materials for fractured reservoirs

Thesis Type: Postgraduate

Institution Of The Thesis: Middle East Technical University, Faculty of Engineering, Department of Petroleum and Natural Gas Engineering, Turkey

Approval Date: 2019

Student: Uğur Gargılı



The lost circulation is a primary consideration while drilling through fractured carbonate formations. Uncontrolled lost circulation may result in high nonproductive drilling time and cost, stuck pipe, side-tracks, blowouts and occasionally, the abandonment of expensive wells depending upon the severity of the loss. Additionally, drill solids entering the reservoir as a result of lost circulation may plug the pore throats, leading to a significant decrease in production. In the industry, there are two approaches to struggle with loss circulation; to treat (control and stop) losses after they occur, or alternatively strengthen the loss zones to prevent losses. Indeed, it has been proved that it is easier and more effective to prevent occurrence of losses than to attempt to control and stop them once they started. Preventive method is also known as wellbore strengthening. The method aims to both alter stresses around wellbore and minimize fluid loss. They are effective not only on natural fractures but also induced fractures which occurs during drilling. The objective of this study is to determine optimum concentration and particle size distribution for fractured reservoir zones. A polymer-based reservoir drill-in fluid supported by wellbore strengthening materials (WSM) was used in this study. Sized ground marble (GM) was chosen as a WSM because of its hydrochloric acid solubility and reservoir non-damaging nature. Sized GM was used as a WSM in different concentration and in different particle size range. The experiments were conducted by using Permeability Plugging Apparatus (PPA). Fractured formations were simulated by using metal slotted disks with fracture width of 400, 800 and 1200 microns. Tests were conducted at room temperature (about 20 to 25 degrees Celcius). During the study, a total 269 tests are run to investigate the effect of different particle size distribution, concentration and fracture width. The results have been compared according to maximum sealing time required to reach assumed pressure and fluid loss values, therefore, optimum composition has been determined.