Su Bazlı Sondaj Sıvılarının Termal Döngü Testine Dayalı Termal Stabilitesi

Abstract

Thermal stability of water-based drilling fluids is an essential factor especially through drilling geothermal and deep oil and gas wells. The chemical and physical properties of a drilling fluid system are substantially affected by high temperature and consequently lead to excessive gelation and formation damage issues. As a result of high temperature, formation damage might result from high fluid losses and reaction with formation fluid salts and hydroxides. This study is an attempt to investigate the thermal stability of clay base drilling fluids using thermal cycle testing. This test is a part of stability testing that allows determining if a fluid system remains stable under various conditions. This type of test can be applied to the drilling fluid systems and puts the sample through a series of extreme and rapid temperature change encountering in during fluid circulation in a geothermal well. Less toxicity as well as commercial and economical availability of clays make them an inevitable component for drilling fluid systems. A type of sepiolite clay taken from Eskisehir in Turkey and Wyoming bentonite as the API reference clay were considered to prepare freshwater weighted, unweighted, and solid contaminated fluid systems. API recommended and oscillation amplitude sweep tests were firstly carried out to evaluate the mechanical stability of selected fluid systems. The samples were then subjected to five thermal cycles from 25° C to 150° C. The relative change of the viscosity value compared to the value at the start of the thermal cycles was used as a measure of the structural changes in the fluid systems. The sample that shows a small value for the relative structural change at the end of the thermal cycles has the lowest decrease in the viscosity and hence the highest thermal stability. Discovery Hybrid Rheometer (DHR-II) was used to apply the oscillation and thermal cycle testing. Results revealed that sepiolite based muds formulated in this study tolerate stability problems resulted from high and rapid temperature variation. Obtained appropriate thermal rheological properties as well as thermal cycle test results were strong indicators for the effectiveness of sepiolite muds. This study can help the oil and geothermal industry to be more familiar with a high-temperature stable sepiolite clay to prepare high-performance drilling fluids.

RETRACTED: On Improving Water-Based Drilling Mud Swelling Control Using Modified Poly(Vinyl Alcohol)s

“…One of the main challenges when drilling deep wells is the thermal stability of the drilling mud. 3 As temperatures rise, the drilling fluid viscosity, for example, decreases and eventually increases drilling equipment wear and tear. Water-based drilling mud (WBM) is preferably used in over 80% of wells for high-temperature (HT) resistance.…”

“…However, this WBM feature still shows essential limitations, 9 as several experimental studies reported the high sensitivity of drilling mud properties under high conditions. 3 , 10 Ayotunde (2014) reviewed that the rheological properties of WBM do not always remain constant, which is undoubtedly a precursor to drilling challenges. These properties include mud density, viscosity, yield point, and gel strength.…”