Improvement of Gas Recovery Factor Through the Application of Dewatering Methodology in the Huamampampa Sands of the Aguaragüe Field

Abstract

The Huamampampa formation is one of the best gas reservoirs of Devonian basin located in the North-West of Argentina. In the Aguaragüe field, this natural highly fractured reservoir has produced a large amount of gas, even after most of the producing wells became watered-out. An excellent improvement of gas recovery factor has been achieved by the implementation of an unusual dewatering methodology. The method consists of applying a gas-lift production system to extract water from each flooded well. This type of exploitation causes a delay of the wells water encroachment and an increment of matrix gas production through the wells located at the top of the structure. In this paper we show the benefits of the implementation of this gas exploitation scheme as applied to the field. There have been numerical simulation studies performed in different stages of the exploitation and by different authors. The last study takes into account a vast gas and water production history. Different exploitation cases have been analyzed. The sensitivity scenarios presented here demonstrate the need and the benefits of dewatering. Introduction The Aguaragüe field is located in the Devonian basin to the North-West of the province of Salta in Argentina. This gas tramp is an anticline (Figure 1) originated by forces pushing from the West which generated a number of thrust faults. Huamampampa formation is a gas bearing, low porosity and highly fractured quartzite sandstone. This formation is one of the best gas producers in all the basin. Gas is produced through a network of natural fractures. The formation average section I (with layers BS1, BS2 and BS3), section II (layers BL1 and BL2) and Section III (layers BL3, BL4 and BL5) (Figure 2). BS2, BL1, BL3 and BL5 are the potential producer fractured sands, while the remaining BS1, BS3 and BL4 are considered as not producers layers. Almost all Aguarag e wells completed in Huamampampa produced gas only from layers BS2 and BL1. The field gas production started in 1979, with Cu.x-2 well, which had an initial rate of 500,000 m3/d. Since the discovery, 13 productive wells have been drilled in the structure, reaching a maximum field gas production of 4,000,000 m3/d in 1985 (Figure 3). At this stage the field produced very little water, that is associated to condensed water coming from the gas stream. However, the structurally lower wells had to be abandoned because of a sudden formation water intrusion. Since 1993 the advance of water has been evident and continuous, consecutively flooding wells located in an intermediate position. During the end of 1995 wells started to be converted to water producer through the implementation of an artificial gas-lift extraction system. Currently, only three gas producers remain active, besides a new well (Ag.ap-1001) is about to be completed in Huamampampa formation. At that time, when water started watering out the wells, gas production started to go down very quickly. So, after studies and a numerical simulation, the dewatering methodology was implemented. Thanks to this exploiting methodology we have gotten to keep gas production from crestal wells, and so increase the recovery factor of the field. Present Huamampampa gas production is around 1,000,000 m3/d, with a water rate of 1,400 m3/d coming from dewatering. Lately, we have made a numerical simulation work, which was used to study the reservoir drainage mechanism, dewatering performance and optimization. This model and its results are described below.