Reduced Productivity Impairment For Fracture Stimulated Gas Condensate Wells
Authors: Carlson M.R. , Myer J.W.G. 
Published: March 2010

Development of a retrograde condensate reservoir requires accurate well productivity predictions for a capital commitment to gas processing facilities. Historically, Fussell(1) identified that liquids condensing in the reservoir will result in a substantial productivity impairment. A single well model, which included a hydraulic fracture as part of the grid system, was developed to perform sensitivities for well test interpretation and to predict long term performance. Interesting results were obtained. The productivity of fractured wells was not impaired to the degree expected. Radial modelling confirmed the results obtained by Fussell. Current simulation technique allows for direct modelling of a hydraulic fracture instead of using an equivalent well bore radius. The distribution of pressure drawdown and condensate dropout around a hydraulic fracture results in limited productivity impairment. The methodology used and the results obtained are described.

Introduction

This work was originally completed to forecast production from wells in a new field, which was being developed in the Deep Basin area of Alberta, Canada. This study was comprised of geological review, PVT characterization, numerous well test sensitivities, as well as simulating the effects of condensate dropout on well productivity. The ultimate objective of this work was to make a nomination for a sour gas plant.

This paper concentrates on the most important technical point which is that the productivity of wells, which are hydraulically fractured, may not be as adversely affected by condensate precipitation as was previously reported. However, in any actual study, there are a significant number of factors which are derived from different disciplines within petroleum engineering, which must be integrated. We have therefore placed our main results within an abbreviated outline of the process used in solving an actual field problem. In the authors' opinion, this is more valuable to practicing engineers.

As much as possible, the material is presented chronologically so as to follow the development of the technical work. Material is presented under the following major headings: Geological Review, PVT Characterization, Model Construction, Well Test Modelling, Effects of Condensate Dropout, and Conclusions. Originally this work was completed for a single well, which was later expanded to include other wells in other pools. Only the work done on the first well analysed is presented and does not apply universally to the area.

Geological Review

The main objective of this phase of the study was to develop a quantitative reservoir description. This included porosity, permeability, water saturation and layering (heterogeneity). Since this was a new play, relatively little information was available on this zone.

The lithology of the sandstone in this well was derived from a core description. Overall, the sand comprises interbedded dark grey-black shaley siltstones and light grey dolomitic sandstones. The shaley siltstones occur in beds that range in thickness from centimetres (inch) to metres (3 to 6 ft.). The sandstone occurs in beds 1/10 of a metre (4 in.) to metres (3 to 6 ft.) thick.

Layering can be a major consideration in the design of a simulation, particularly for secondary recovery.