D50 Shift Factor – Shifting the Concept of SBMs Performance Evaluation

Different grades of sized bridging materials such as ultra-fine, fine, medium and coarse grades are frequently used in drillin fluid formulations to enhance fluid characteristics, improve mudcake quality and eliminate or reduce formation damage while drilling. Selection of high quality and long lasting SBMs is an essential part of superior drill-in fluid design to achieve these goals. Historically, color, provenience or origin of the SBM samples were evaluated visually or by applying some geological analysis tools such as the petrographic tools to identify and select highly durable and mechanically strong SBM products. These subjective and inappropriate methods of assessment frequently lead to disastrous SBMs performance in down hole conditions. Due to the limitation and ambiguity of the petrographic methods, attempt was made to identify high quality and long lasting SBMs by evaluating acid solubility of SBMs. Though this evaluation criterion is good from acid solubility point of view, it has no relevance to mechanical behavior of SBMs while drilling. Hence, the assessment method also provided misleading information regarding SBMs performance in down hole conditions. Due to the failure of the above approaches, attempt was made to assess SBMs quality using Brinnel Hardness Tester. The outcome of the research was not reliable and inconclusive and thus was not successful in providing a guiding tool for SBMs performance evaluation. This paper describes a fit-for-purpose index parameter defined as the D50 Shift Factor that readily indicates the relative toughness of SBM products and thus provides a powerful guiding tool for high quality SBM product selection for superior drill-in fluid formulations. The index parameter is based on size degradation principle of SBM particles i.e. weak SBMs will cause higher shift of the D50 size compared to tough SBM products. Experimental results demonstrate the usefulness of the D50 Shift Factor in SBM performance evaluation and superior fluid formulations for trouble-free, economic and nondamaging drilling operation.