Cement bond evaluation using well logs: A case study in Raniganj Block Durgapur, West Bengal, India

Cement bond logs (CBL) and variable density log (VDL) are one of the vital logging techniques used to evaluate cement-casing-formation bonds before the well testing or execution of the production operation in the well. These logs are also crucial during the workover operation to maintain the integrity of the well. The logging techniques provide a clear view of the quality of cement bonds with casing and formation. The microannulus and other deviations in bonding between the cement and the casing or formation are recorded using this technique. Therefore, this technique is used by the regulatory authorities worldwide for the determination of the cement bond with casing and formation. In this paper, the CBL/VDL logging technique was used to determine the bonding between cement and casing and cement and formation at two different CBM wells from 850 to 1600 m depths in the Raniganj block of Durgapur, West Bengal. Two well, namely, A and B, were analyzed to determine the cement-casing-formation bonds in the study area's coal seam zone. The analysis was carried out at normal and pressure pass to investigate the integrity of the well using the CBL/VDL data. The normal and pressure pass in well A indicated the presence of microannulus in the bonding between cement and casing/formation in the coal seam zone. The corresponding analysis of well B showed poor cement and formation bond at the coal seam zone during the normal pass but good bonding after the pressure pass. Thus, it was observed that the CBL/VDL data were capable of determining the cement-casing-formation bonds in both the well of the study area and the well's integrity.

Improving Cement-to-Pipe Bonding Evaluation on Coated Casing

ABSTRACT In the Oil and Gas industries, drilling a well in both exploration and development operations is becoming more challenging due to the reservoir location and complex reservoir system. A sophisticated high-cost well structure with complex trajectory, subsea system, or even operating in deep water is sometimes unavoidable. One of the crucial factors for a successful well construction operation is to achieve excellent well integrity by having good zonal isolation throughout the target reservoir section. This requires flawless primary cementation from cement job planning, design, and up to execution. The cement bond quality will need to be evaluated by performing the post job cement execution evaluation and wireline logging cement bond log survey. Supported with more stringent regulations, well integrity is becoming a fundamental aspect in drilling and production operations. This brings new challenges to cementing operations and subsequent cement evaluation. Flawless primary cementation is of great importance, from the job planning, design, to the execution. Post-job cement evaluations are needed by performing Pressure Match Post-Job Analysis and Wireline Logging Cement Bond Log Survey. Key parameters in designing optimum zonal isolation cement slurry is good understanding of the wellbore technical challenges and mitigating all geological and formation-related risks, such as narrow pressure margin, gas migration risk, etc. Light cement, complicated cement composition recipes, small cement - mud weight ratio are more common these days, supported with the developing technology in cementing. These, on the other side, would impact the cement bond evaluation. Good cement bond is crucial to ensure good zonal isolation across the reservoir intervals. Casing external coating, applied to protect casing strings from rusts, is another aspect affecting the cement bond, especially cement-to-casing bond. A more advanced cement bond evaluation tool will be required to cope with variety of cementing conditions, to enable producing undoubted log results. Thus, helping Operator in making decisions of subsequent well operations. This paper shows and presents different cement bond log interpretation results from four wells executed with a different method of implementations, performed in a development drilling campaign in Natuna Sea, offshore Indonesia in year 2019. The paper will focus on the 9-5/8" casing cementation, on which the cement bond evaluation became one of the main attentions.