Abstract

There are two major challenges in achieving perfect and durable inter/intra zonal isolation; accurate planning of cementing operations according to well specific requirement and realistic evaluation of operational performance for attainment of the objective. Prevailing practice for evaluating cementing performance , in the industries is not authentic enough to justify remedial operations planned. It just based on readings of graph while other critical aspect such as phenomenal formational response, influence of other processes which are being performed / to be performed prior to or post cementing operations like hermetical testing of casing, various activation/stimulation processes which could affect the quality of evaluation/performance are overlooked.

The objective of study is to address all the relevant aspects while interpreting the logs and develop a methodology for making precise and realistic evaluation of logs for avoiding many futile operations which ultimately affects the productivity and life of the wells.

  • The procedure adopted for formulation is as under

  • Compilation / analysis of log data field wise

  • Compilation / analysis of production trend with reference to cementing performance.

Mathematical model exhibiting impact of stresses produced during pressure testing at various stages of cementing through well completion process and its influence over logs and cement bond integrity.

Influence of formational image on sonic log graph.

Organization of all logical and mathematical data to design and develop realistic-precise methodology.

This paper provides

  • an innovative approach to the prevailing practice

  • helps to develop a methodology which may utilize all those data presently ignored

  • to devise a precise diagnostic tool in the form of software to reduce human error, this is under conceptual stage.

This methodology may limit its application to the development field as exploratory wells may not have sufficient quantum of data for uploading in the software for analysis.

Introduction

Primary cementation of hydrocarbon wells has its own importance when life and health of producing, depleting or high WOR /GOR wells is a topic of discussion. It is always a point of emphasis and concern when well is cemented and evaluated for the first time.

Cement bond log tool or any other tool of this category reads the sonic signals in terms of time and/or amplitude (magnitude) of sonic wave returned from the structure around the casing pipe. This graph is then evaluated based on curve readings and using empirical formula for finding out percentage bonding achieved. The cement bond measurement principle is based on acoustic wave attenuation and impedance viz "when cement sheath firmly bonded to the casing and formation can intuitively attenuate sound propagation in the complex media around; responsible for wave propagation". CBL tool is able to differentiate between "no cement" and "solid cement." range for comparison and individual opinion but not for evaluation. These tools are not able to provide unanimous answer to the question - whether cement job will prevent fluid flow in the annulus or not? The chief problem with acoustic-type CBL tools is that the casing-signal attenuation is not directly related to the degree of hydraulic sealing provided by the annular cement. Hence, no matter how accurately the attenuation is measured, answers are still in terms of probabilities and uncertainties. Even though this tool is widely used in interpretation purpose.

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