Cement Evaluation in Highly Laminated and Multi-Stacked Sandstone Reservoirs: The World First Novel Approach Using Dual-Physics Cement Bond Assessment

Abstract

Advances in cement recipe, additives and cementing technology including light weight cement, ultra-low fluid loss cement blend and improved cement to mud rheology mixing to seal the continuous liquid channels have prompted the industry to find an innovative way to evaluate the cement bond and integrity with a more robust and integrated approach. Evaluating cement bond behind casing based on single tool platform had shown some inherent uncertainties mainly due to borehole effects, tool eccentralization and processing variation. This paper will highlight few case studies on the application of both electromagnetic acoustic wave (EMAT) and ultrasonic cement evaluation logs including the world's first tool combination in single run to enhance understanding on cement integrity and optimize the perforation interval for production. Channeling and microannulus occurrences whether dry or wet are the most common features in cement integrity evaluation and yet poorly characterized to prevent any unwanted cross-flow or adverse impact to production. Electromagnetic acoustic wave cement evaluation in combination with an ultrasonic tool allow direct quantification of compressional, shear and flexural attenuation properties of cement downhole as well as acoustic impedance and microdebonding feature of the cement. Separation between average shear and flexural attenuation curves may indicate presence of microannulus depending on the extent of the separation without any requirement of additional pressurized logging pass. Parameter threshold determination based on shear and flexural attenuation cross-plot also indicates severity of cement microdebonding. Results showed that good production rate with lower water cut and low GOR reading had been achieved from specific perforated zones in the well. Electromagnetic acoustic wave and ultrasonic cement evaluation tools had successfully defined the zonal isolation layers as thin as 2 to 3 meters along the wellbore and optimized the perforated zones to avoid any liquid channeling or premature water and gas breakthrough into the wells, which can affect the production attainability and drainage efficiency from particular reservoirs. In a nutshell, combination of EMAT acoustic wave and ultrasonic cement evaluation principles prove to provide a more comprehensive overview on the cement bond integrity behind the casing. Having two independent downhole measurement which complement each other will reinvent the effort in cement bond assessment for complex reservoir environment which is susceptible to interpretation ambiguity.