| Title | Controlling Rheological and Fluid Loss Properties of Sepiolite Based Muds under Elevated Temperatures |
|---|---|
| Authors | Gursat Altun, Ali Ettehadi Osgouei and Umran Serpen |
| Year | 2010 |
| Conference | World Geothermal Congress |
| Keywords | Sepiolite, Geothermal drilling, Mud, Salinity, HTHP, Mud additives, Turkey |
| Abstract | Geothermal well drilling is known as high temperature environment; therefore, it is difficult to formulate a drilling mud functioning adequately, particularly in temperatures above 100 oC. Circulation breaks, abnormally high fluid losses and viscosities, and unacceptable high gel strengths are the main problems that are usually associated with geothermal wells. Although bentonite based mud with extremely expensive additives is commonly used in these drilling conditions, it does not meet the desired needs in higher temperatures above 150 oC. There are geothermal fields having temperatures more than 240 oC in both Turkey and the world. Therefore, sepiolite, a magnesium silicate clay mineral with fibrous texture, has been proposed as the bentonite replacement for both the high temperature and the high salinity environment. There might be temperature dependent minor changes in crystalline structure; nevertheless, sepiolite is stable at temperatures up to 260 oC. Additionally, the basic structure of sepiolite is known to be firm in saturated saline-water phase. Turkey has the largest sepiolite clay deposits in the world; on the other hand, the usage of sepiolite clay as a drilling fluid not only in Turkey and but also in the world is negligible. This study is an attempt to characterize both rheological and fluid loss behavior of water-based drilling fluid prepared with five different raw sepiolite clay samples obtained around Sivrihisar-Eskisehir district of Turkey. The samples were not treated or purified by any chemical methods before and after grinding. API standards were followed throughout the experimental study. No additives other than salt have been used while formulating sepiolite muds to determine the rheological and filtration properties. Four out of five samples in ambient conditions have given better rheological property than that of indicated by the API standard. One of the four samples satisfying the requirement was selected and used later in the study along with additives. The results have indicated that the sepiolite based drilling fluid is superior to the bentonite based drilling fluids in terms of both rheological and fluid loss properties under elevated temperature and pressure conditions, particularly at high salt concentrations. |