AVO analysis aids in differentiation between false and true amplitude responses: a case study of El Mansoura field, onshore Nile Delta, Egypt

Abstract

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.

New AVO Attributes and Their Applications for Facies and Hydrocarbon Prediction: A Case Study from the Northern Malay Basin

“…Wavelet and seismic ties were important in forwarding modeling to generate an actual earth model. The match was based on a selection wavelet that created for predicting the model response [5]. The well-seismic tie depended on measuring the density and sonic logs in generating an acoustic impedance log [17].…”

“…The seismic AVO was extensively used in facies prediction and fluid parameter studies [5]. The AVO attribute was commonly applied to illustrate the relationship between rock physical properties and seismic [19].…”

“…Real seismic data, pre-stack seismic data including near, mid, and far, then well log data were integrated to get suitable identification on facies and fluid. The AVO analysis was created by extracting intercept (A) and gradient (B) to be applied as Scaled Poisson's Ratio change and the new AVO attributes (SQp, and SQs), which created cross plots to classify reservoir fluids and lithological units [5]. The seismic gather was used as an input for AVO common attributes, including intercept (A) and gradient (B), which was applied by two-terms of Aki-Richards (Figure 6).…”

“…The data integration by applying the amplitude versus offset (AVO) technique is suggested as a method in validating anomalies of seismic amplitude associated with gas sands [4]. AVO analysis is extensively used in lithology characterization, hydrocarbon detection, and fluid parameter analysis [5].…”

“…The facies proposition is classified by using the cut-off of some logs e.g., volume of shale, volume of coal, water saturation, and porosity. In the seismic scale, the seismic AVO is extensively used in hydrocarbon prediction and fluid parameter studies [5]. The Scaled Poisson's Ratio attribute is commonly used in hydrocarbon and facies separation.…”