ABSTRACT

Salt-paste cementing has long faced several challenges including narrow density window, high eccentricity of pipe string, small displacement rate, which make it difficult to ensure an adequate cementing quality. Research has been conducted on reaming technology, small collar casing and managed pressure cementing to alleviate these problems. In this work, research in the use of reaming mode, reaming size, casing collar size, managed pressure cementing mode and application has been carried out to develop a set of complex salt paste cementing techniques. This technology was then successfully applied for the first time in well BZ-X in the Kuqa Piedmont, achieving a great breakthrough in the cementing quality of salt-paste layer in this area, and providing a strong reference for similar complex salt-paste cementing at home and abroad.

INTRODUCTION

The salt-paste layer is a type of high-quality cap layer of oil and gas reservoir, widely distributed in Santos Basin of Brazil, Gulf of Mexico of the United States, Missan oilfield of Iraq, and Kuqa piedmont of Tarim oilfield of China (Zhang, 2018; Wang, 2019; Tian, 2021; Zou, 2021). The salt-paste layer has strong creep property and complex lithology composition, high pressure brine layer and weak layer coexist, resulting in frequent complications, such as stuck drilling, leakage, and overflow. Due to the influence of these geological features, the salt-paste cementing has long been faced with challenges such as narrow density window, high eccentricity of pipe string, small displacement rate and easy channeling in annulus, which make it difficult to guarantee the cementing quality, especially in the Kuqa piedmont.

The salt-paste layer in the Kuqa piedmont has a depth of 3000∼6000 m, a thickness of 400∼1000 m and has a fast creep rate. High pressure brine layer (pressure coefficient 2.10∼2.55 g/cm3) and weak layer (pressure bearing capacity between 2.05-2.20 g/cm3) coexist in the salt-paste layer (Zhou, 2017). The no-collar casing is usually used to seal the salt-paste layer. However, the centralizers cannot be matched in this type of casing, resulting in severe eccentricity and poor displacement environment. In addition, the salt-paste cementing also faces other problems such as small slurry density difference (≤0.05g/cm3) and low annular velocity (0.6∼0.8 m/s), that conventional cementing technical measures are difficult to effectively solve. Between 2017 and 2021, the rate of cementing quality of salt-paste layer in the Kuqa piedmont has been less than 50%.

This content is only available via PDF.
You can access this article if you purchase or spend a download.