Designing a pragmatic solution for complex numerical modeling problem in thinly laminated reservoirs

Alireza Hajizadeh,Raj Deo Tewari,Kokulananda Al Mudaliar

doi:10.1007/s13202-019-0662-5

Alireza Hajizadeh, Raj Deo Tewari + Show 1 more

Open Access

https://doi.org/10.1007/s13202-019-0662-5

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Abstract

Unquestionably, water breakthrough into the producing wells is one of the biggest threats to the development and production of oil and gas reservoirs around the world. The predicted water production profile from a numerical simulation model directly affects the estimated recoverable volumes and hence the decision making process for the field development and the facility design to handle the produced water. The problem of reliably predicting the water production profile exacerbates when dealing with thinly laminated sand reservoirs. Calculating the total water saturation (SWT) using well log data in the hydrocarbon zone in this type of reservoirs is adversely affected by the convoluted readings of the conventional logging instruments whenever the resolution of the laminations goes beyond the tool resolution (i.e. 0.5 feet). This in turn leads to unrealistic movement of water in the model, pre-mature water breakthrough, pessimistic forecast of oil and gas and over-estimation of required water treatment system capacity. Although some advancement has been made in the identification of these types of reservoirs, their reservoir modeling still remains a challenge for petroleum industry due to limitations in developing proper methods to estimate petrophysical properties using conventional logs and also the computational cost of running extremely fine numerical models. In this study various issues and challenges of modeling these types of reservoirs are addressed. A workflow for numerical modeling of thinly laminated sands at affordable vertical grid resolutions has been proposed that properly uses the available geological, petrophysical and engineering data in an effective (vs. total porosity) system. The methodology of reproducing the volumetrics and capturing heterogeneity at various scales, through proper rock-typing and use of net to gross ratios are discussed in detail. The data requirement for modeling, reservoir management and performance monitoring of thin beds is also elucidated. The presented workflow provides a simple yet pragmatic tool that can help best represent the thinly laminated sands at affordable measurement and computation costs, mitigate the risks associated with thin bed reservoir development and increase the value of field development planning.

Highlights

Bedded sandstone reservoirs as a type of low resistivity low contrast (LRLC) reservoirs pose a big challenge for characterization and modeling to the field development planning (FDP) teams in oil and gas industry
A proper rock-typing based on hydraulic flow units (HFU), reconciliation between HFUs and geological rock types and use of a net to gross ratio, is key to modeling of thinly laminated sands
It is shown that using such approach the problem of early breakthroughs is resolved; the larger scale heterogeneity could be reproduced effectively by defining HFU based rock types while the velocity of fluids can be captured though use of net to gross in the calculation of transmissibility

Summary

Introduction

Bedded sandstone reservoirs as a type of low resistivity low contrast (LRLC) reservoirs pose a big challenge for characterization and modeling to the field development planning (FDP) teams in oil and gas industry. Thin laminated sands can be recognized from core samples (Fig. 1) during the appraisal stage of the field. This type of LRLC reservoirs cannot be readily identified from log information, they are clearly visible on whole cores. Techniques such as Synergetic High-Resolution Analysis and Reconstruction for Petrophysical Parameters (SHARP, a Schlumberger technology) have been used in some FDPs to enhance the conventional logs for deep resistivity (Rt), density (RHOB) and neutron (NPHI) logs. Further information on evaluation and characterization of thinly bedded sands can be found abundantly in the literature (Bastia et al 2007; Michel et al 2006; Yadav et al 2010)

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