Abstract

Digital well log and 3D pre-stack seismic data are combined to improve reservoir characterization. 3D seismic pre-stack gathers contain significant information about lithology, rock properties and fluid content. The biggest challenge is to integrate log scale geologic information with seismic scale measurement of the same geological unit. Gulf Coast geoscientists have actively been using integrated seismic gathers and well logs in AVO and inversion analysis for decades. Rocks of the mid-continent have often led us to discount, or even dismiss completely, the analytical capabilities of onshore seismic gathers. Traditionally, rock properties are estimated from elastic inversion results using neural networks. This article discusses a method that utilizes the power of digital log analysis, LambdaRho/MuRho innovative cross plots and integration with seismic pre-stack gathers to predict rock properties in the unconventional reservoirs.

Introduction

Drilling and producing of unconventional reservoirs have been considered a "mining" operation for many years. The general thinking was that is more important to secure land leases over areas that seem to produce higher yielding wells than spending money and time on science projects. After all, the shale deposits are widespread and no large variation in production was expected. However, this was proven to be unrealistic and the value of seismic data are now recognized. Seismic data, especially attributes derived from pre-stack data are now extensively used to design and execute lateral drilling programs as the reservoirs have a much larger heterogeneity than expected. Higher producing wells characteristically are drilled into shales with higher Total Organic Content (TOC) and more favorable rock properties like porosity and elasticity which is a measurement of how easy the rock cracks during fracking and opens space for the hydrocarbons to flow towards the pipe. Carbonate units can be embedded within the producing shale units and the pre-drill knowledge of their locations is very useful when designing the lateral drilling path.

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