Production Performance of a Retrograde Gas Reservoir: A Case Study of the Arun Field

Abstract

SPE Members Abstract The Arun field is one of the world's giant retrograde gas reservoirs. Approximately 10 years after production began, a significant loss in well productivity occurred in some of the wells. The study shows that this productivity loss was due to near wellbore condensate accumulation, and documents its effects on production and pressure transient response. A radial, single well, compositional model was used to study this effect and confirm that the productivity loss was due to liquid accumulation. The model was also used to predict the future performance of the well. The model matches well production data and the pressure transient response of affected wells. This work identifies near wellbore condensate accumulation as an extremely important factor to consider when predicting future well performance as some of the productivities are reduced by 50%. The work also details how production data and well test analysis can be used to quantify the effects of near wellbore condensate accumulation on well productivity. Introduction The engineering aspects of gas condensate well performance have been a subject of research and development for many years. Recognizing that classical analytical methods (such as Al-Hussainy, et. al. and Govier) for dry gas wells do not apply for two phase conditions of a gas condensate well, several semi-analytical and numerical methods were developed. Here, our intention is not to present an exhaustive literature review. However, the reader is referred to Chopra for some reference to prior work. In this paper we present the application of compositional modelling to pressure transient response of wells affected by condensate dropout, and to predict future well performance. The Arun field is one of the world's giant retrograde gas reservoirs. Well test analyses indicated possible liquid accumulation effects. This was confirmed with well productivity plots. A conceptual, single layer compositional model was used to verify that liquid accumulation would cause the same type of behavior observed in the field. Subsequently, a multi layer compositional model was used to model a specific well. Background The Arun field is located on the northern coast of Aceh Province in North Sumatra, Indonesia (Figure 1). Mobil operates the field, which began production in 1977. The average reservoir pressure and temperature were 7,100 psia and 352 F at a datum elevation of 10,050 ft-ss. The reservoir is a thick limestone formation with a thickness of over 1,000 ft in local areas and covers a productive area of over 23,000 acres. The initial condensate to gas ratio (CGR) was 65 Bbl/MMscf at separator conditions of 1,250 psia and 68 F. P. 73^