An Experimental Study on Structural and Thermal Stability of Water-Based Drilling Fluids

Yıl 2021, Sayı: 23, 70 - 80, 30.04.2021

Ali Ettehadi

https://doi.org/10.31590/ejosat.843568

Öz

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 are 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.

Anahtar Kelimeler

Drilling fluid, Thermal stability, Sepiolite, Thermal cycle

Destekleyen Kurum

Scientific and Technological Research Council of Turkey (TÜBITAK)

Proje Numarası

217M723

Teşekkür

The authors would like to sincerely thank the Scientific and Technological Research Council of Turkey (TÜBITAK-217M723) as the lead sponsor of this R&D project.

Su Bazlı Sondaj Sıvılarının Yapısal ve Isıl Kararlılığı Üzerine Deneysel Bir Çalışma

Öz

Jeotermal, derin petrol ve gaz kuyularının sondaj operasyonlarında su bazlı sondaj çamurların termal stabilitesi (ısıl kararlılığı) oldukça önemli bir parametredir. Sondaj akışkanının kimyasal ve fiziksel özellikleri, yüksek sıcaklıktan önemli ölçüde etkilenmekte ve sonuç olarak bu durum aşırı jelleşme ve formasyon hasarı sorunlarına yol açmaktadır. Yüksek sıcaklığın sonucu olarak, formasyon hasarı, yüksek sıvı kayıpları ve sondaj sıvısının formasyondaki tuzlu su ve hidroksitlerle etkileşiminden kaynaklanabilmektedir. Bu çalışmada, kil bazlı sondaj çamurlarının termal stabilitesi termal döngü testini kullanark incelenmiştir. Bu test, akışkan yapısının farklı koşullar altında kararlı kalıp kalmadığını gösteren etkin bir stabilite (kararlılık) testi olarak bilinmektedir. Bu test, jeotermal ve derin petrol ve gaz kuyularında sondaj akışkanının karşılaştığı ani ve hızlı sıcaklık artışlarını canlandırmak için sondaj akışkanına bu çalışma kapsamında uygulanmıştır. Çok az toksik etki göstermesinden, ekonomik uygunluğundan ve kolay bulunabilirliğinden dolayı killer sondaj akışkan sistemleri için kaçınılmaz bir katkı maddesi olarak tanınmaktadır.
Eskişehir, Türkiye’den alınan sepiyolit kili ve API referanslı Wyoming bentonite kili, saf su kullanılarak; ağırlaştırılmış, ağırlaştırılmamış ve kirletilmiş çamur örnekleri hazırlanmıştır. Osilasyon genlik süpürme testleri öncelikle seçilen akışkan örneklerinin mekanik kararlılığını incelemek için uygulanmıştır. Ayrıca hazırlanan örnekler 25 °C den 150 °C ye kadar artarak oluşan beş termal döngü testine tabi tutulmuştur. Termal döngü testinin başlangıcındaki değere kıyasla viskozite değerinin göreceli değişimi, akışkan sistemlerindeki yapısal değişikliklerin bir ölçüsü olarak kullanılmıştır. Termal döngü testinin sonucuna göre, en az değeri göreli yapısal değişim gösteren çamur örneği, viskozitede en küçük düşüşe ve dolayısıyla en yüksek termal stabiliteye sahiptir. Discovery Hybrid Rheometer (DHR-II) aleti, osilasyon ve termal döngü testlerini uygulamak için kullanılmıştır.
Bu çalışmanın sonuçlarına göre, formüle edilen sepiyolit çamurunun yüksek ve ani sıcaklık değişimlerine karşı stabilitesini (kararlılığını) koruduğu gözlemlenmiştir. Elde edilen uygun termal reolojik özellikler ve termal döngü test sonuçları, sepiyolit çamurlarının etkinliği için güçlü bir göstergedir. Bu çalışma, yüksek performanslı sondaj sıvıları hazırlamak için yüksek sıcaklığa duyarlı olan sepiyolit kilinin petrol ve jeotermal endüstrisinde daha fazla tanıtımına ve kullanılmasına yardımcı olmaktadır.

Anahtar Kelimeler

Sondaj Çamuru, Termal Stabilite, Sepiyolit, Termal Döngü

Proje Numarası

217M723

Kaynakça

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