Inclusions of well test interpretation and sector model simulation into a full field model: an integration modeling approach
Authors: Al-Mohannadi Nasser Saqer , Seybold Oliver Maximilian , Reijnders Gert-jan C.A. , Dawans Jean-Michel Laurent 
Published: December 2009

In greenfield developments, production test data is often the only data available (other than analogues) that can be used to constrain dynamic reservoir behaviour. However, often the integration of production well-test data and its interpretation into the static and dynamic reservoir models is limited to the incorporation of the calculated Kh and skin values.

A well-test of a gas bearing carbonate formation of a well drilled as part of a gas development drilling campaign is used. In addition, a care is taken to include well-test results into the static and dynamic reservoir models. This is because relatively coarse-gridded simulation models cannot reproduce detailed well inflow behaviour due to the lack of discretization. As a result, the assumption of directly using well properties (kh and skin) determined from analytical well-test analysis in coarse gridded simulation models may not hold for all physical environments, particularly in the near-wellbore behaviour. Well-tests can be matched with detailed fine gridded single well models, which then should be used to upscale the well properties for coarser grids. The study illustrates how these "pseudo-well properties" can change as a function of full field simulation grid size and permeability thickness product (kh). In addition, this is done with out incorporation of the viscous stripping effect and the detailed geological features such as small fractures, warmholes on the condensate behaviour of different grid sizes.

Introduction

One of the challenges in building static and dynamic reservoir models is the aspect of upscaling. The right balance is sought between the preservation of geological resolution, accurately representing of physical behaviour and the required computational time to generate dynamic simulations. However, where in the process of upscaling due attention often is paid to the correct preservation of the geological properties, less attention is paid to the impact of grid coarsening on the calculated near-wellbore behaviour. This paper describes a workflow that was developed to address this issue and the findings of a case study that investigated the impact of matching well performance observed in production tests as a function of the grid size. In addition, this workflow may lead to a significant improvement in the prediction of future well productivity particulary in the near-wellbore flow.

The workflow and the possible impact of this well-test interpretation approach on production forecasts will be illustrated using well-test results from a gas-bearing carbonate formation wells. These wells are drilled and production tested as part of a gas development drilling campaign located in the North Field.

In this paper, the study focuses on the inclusions of the detailed flow behaviour recorded during well-test in a coarser full field model.

Study Workflow

As well-test transient pressure responses cannot be adequately replicated in a coarse full-field model, an intermediate step was introduced in the modelling workflow wherein, a finely gridded sector model is extracted from the full-field geological model. The minimum wellblock size required to resolve a certain level of detail from well-test can be found based on the radius of investigation (Rinv) of the pressure responses at different times during well-test as shown in Figure 1. It can be seen that 50m wellblock size is needed as minimum to simulate the early time pressure transient responses.