Cement-Integrity-Evaluation Solution in Extended-Reach Wells in the South China Sea
Authors: Carpenter Chris 
Published: March 2016

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper OTC 25027, “Solution to Cement-Integrity Evaluation in Long Extended-Reach Wells: New Record in the South China Sea,” by Jun Cai, Yongde Gao, and Mingjie Zhang, CNOOC, and Lei Cui and Hongzhi Guo, SPE, Schlumberger, prepared for the 2014 Offshore Technology Conference Asia, Kuala Lumpur, 25–28 March. The paper has not been peer reviewed.

The combination of ultrasonic pulse-echo and flexural-attenuation measurements was adopted in this project in the South China Sea for cement-integrity evaluation. This new method aids in understanding why integrity losses occur in certain sections, by analyzing third-interface information uniquely provided by flexural-wave imaging, and in formulating improvement actions for future cementing jobs. This method achieves a more-explicit cement-integrity-evaluation result with detailed graphical annulus information compared with the limited output from conventional acoustic measurements.

Introduction

In the Weizhou field in the South China Sea, most of the development wells are drilled as long extended-reach wells with a deviation greater than 70°. The wells are designed to reach more than 70° deviation at a very shallow depth (approximately 900 m) compared with the total depth of the well (approximately 4500 m). In a typical well, surface casing (13.375 in.) runs beyond the kick-off point and reaches maximum deviation of the well at a shallow depth (approximately 900 m). Intermediate casing (9.625. in.) runs from surface to more than 4000 m, with three different fluids/ slurries pumped in the annulus: regular-weight tail cement (1.90 g/cm3), freshwater displacement cement, and lightweight lead cement (1.58 g/ cm3). The completion liner (7 in.) hangs on the intermediate casing, with 1.90-g/cm3 cement pumped in the annulus.

A campaign was planned to perform cement-integrity evaluation in five wells (A9, A10, A1, A2, and A3). The basic information about these five wells is listed in Table 1 of the complete paper. The objective for Well A9 was to evaluate the 7-in. completion casing, and the objective for the remaining four wells was to evaluate the 9.625-in. intermediate casing. The well profile and completion pose several challenges:

Cementing highly deviated wells has uncertainties associated with cement placement because of the likelihood of poor mud removal, which is generally caused by pipe eccentering.

Intermediate casing is cemented with both regular-weight and lightweight cements. A more advanced method to evaluate the material in the annulus independently of its density is required for this project.

The geometry of casing in the borehole is important information in this type of well because it is the main factor affecting the cement placement in the annulus.

The logging tool string is not able to be conveyed by wireline only because of the high deviation along the wellbore. An alternative conveyance needs to be performed in an efficient manner.to save rig cost.

For a discussion of the conveyance-selection process that resulted in the selection of a wireline tractor, please see the complete paper.