A Novel Methodology for Estimation of In-Situ Relative Permeabilities from Wireline Formation Tester Data in an Abu Dhabi Carbonate Reservoir

Cig, Koksal (Schlumberger Middle East SA.) | Kristensen, Morten Rode (Schlumberger Middle East SA.) | Thum, Sebastian (Schlumberger STS) | Ayan, Cosan (Schlumberger) | Mackay, Eric James (Heriot-Watt University) | Elbekshi, Amer (Abu Dhabi Company for Onshore Oil Operations) | Naial, Radwan (ADCO)

OnePetro 

Abstract         

A multilayer carbonate reservoir, having medium to low permeabilities with distinctive oil-water contacts, is in an appraisal stage. Large data gathering including rigorous coring is underway in the field. It is identified that the slowest part of the data evaluation is generally SCAL analyses due to its laborious workflow. A new approach is proposed by introducing a wireline formation tester (WFT) multiphase flow analysis to obtain relative permeabilities. The WFT tool is commonly used in this field to measure pressures and collect samples. In this paper we present a novel methodology for estimating in-situ relative permeability curves with the help of available WFT multiphase flow data and its numerical optimization.

During drilling of a well the formation is exposed to mud filtrate invasion. The invasion displaces oil in the vicinity of the wellbore, much like a small water flooding experiment in the case of immiscible mud filtrate and formation fluid. A WFT sampling operation in a multiphase flow environment provides an opportunity for determining related properties by utilizing bottom-hole pressure and water-cut data. A numerical model replicates the mud filtrate invasion and sampling with reservoir properties and WFT tool geometry. The numerical simulation model consists of a proper definition of reservoir properties as well as WFT tool geometry, including size and shape of flow inlets, along with tool storage and fluid segregation effects. The model is embedded in an optimization workflow and relative permeability curves, damage skin and depth of mud filtrate invasion are then estimated by minimizing a misfit function between measured and modeled pressures and water-cuts. The relative permeability curves are parameterized using industry accepted models. The optimization workflow uses a distribution function of response parameters where the entire parameter range is included in the numerical runs, thus ensuring that a global optimum is found. Initial parameter estimates are determined from open hole logs, such as resistivity, dielectric, magnetic nuclear resonance and from pressure transient analysis.

The methodology developed in this paper is validated by application to a synthetic dataset with a known solution, and it is subsequently demonstrated on actual field data from a WFT sampling operation. The results of this paper demonstrate that it is possible to reliably estimate multiphase flow properties from WFT sampling data. The key contributions of this study are to show the capability of estimating a variety of multiphase flow properties from routine WFT cleanup data and to establish an automated approach, including a novel inversion methodology, to reduce the turnaround time.

Introduction

A WFT sampling or cleanup operation in a multiphase flow environment gives an opportunity for determining in-situ relative permeabilities and capillary pressures in an inversion workflow by utilizing data recorded downhole. We describe a methodology to estimate multiphase flow properties with the help of numerical simulation and optimization. The numerical simulation model for the mud filtrate invasion and cleanup consists of a proper definition of reservoir properties as well as WFT tool geometry, including size and shape of flow inlets, along with the tool storage and fluid segregation effects. The numerical simulation model mimics the invasion, cleanup and pressure transient events.