The seismic amplitude versus offset (AVO) analysis has become a prominent in the direct hydrocarbon indicator in last decade, aimed to characterizing the fluid content or the lithology of a possible reservoir and reducing the exploration drilling risk. Our research discusses the impact of studying common depth point gathers on Near, Mid and Far-offsets, to verify the credibility of the amplitude response in the prospect evaluation, through analyzing a case study of two exploratory wells; one has already penetrated a gas-bearing sandstone reservoir and the second one is dry sand, but drilled in two different prospects, using the AVO analysis, to understand the reservoir configuration and its relation to the different amplitude response. The results show that the missing of the short-offset data is the reason of the false anomaly encountered in the dry sand, due to some urban surface obstacles during acquiring the seismic data in the field, especially the study area is located in El Mansoura city, which it is a highly cultivated terrain, with multiple channels and many large orchards on the edge of the river, and sugar cane and rice fields. Several lessons have been learned, which how to differentiate between the gas reservoirs and non-reservoirs, by understanding the relation between the Near and Far-offset traces, to reduce the amplitude anomalies to their right justification, where missing of Near-offset data led to a pseudo-amplitude anomaly. The results led to a high success of exploration ratio as the positives vastly outweigh the negatives.

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Mud-weight selection is a critical factor for ensuring wellbore stability while drilling, especially in the presence of unstable shale formations. This paper describes a geomechanical approach that has been used to optimize the drilling of these types of wells. In an offshore field, the 12-¼-in. sections are typically drilled across well-known, unstable shale formations that have caused numerous stuck-pipe incidents and wellbore-related nonproductive time (NPT) in most of the offset wells. During the planning phase, the formation evaluation data, casing design, and directional profiles are reviewed and analyzed. These data are then used to perform a geomechanical study to identify the safe mud-weight window. The outcome of the study is then used to produce a set of guidelines for drilling these wells across the problematic 12-¼-in. section. These guidelines were applied to wells from an offshore field in Saudi Arabia in which the troublesome section was drilled to the casing point in each well, with no observed wellbore-stability issues. There were no losses induced and no formation collapse encountered. The planned reaming trips were eliminated, which significantly reduced the cost of drilling and completing these wells. Based on the outcome of this study and the results, this process, based on geomechanical analysis, can be used as a reference for optimal mud-weight selection to mitigate wellbore-stability problems in nearby platforms in this field of the Arabian Gulf.

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