Optimization of Production Gas Wells by Acidizing Using PLT Interpretation in Hassi R'Mel Field, Algeria

Abstract

The Hassi R'Mel Field is a gas condensate reservoir with three Triassic sands (A-B-C) separated by a thick shale layer. Producing wells were drilled in the Northern-Central-Southern part with two lines of dry gas injection. A decrease in the production wells was observed. Build-up tests realized on those wells showed significant skin, which is due primarily to the excessive invasion mud used during drilling and workovers. A study was undertaken in order to see what method is to be used to optimize and improve the potential of these wells, which is less than hoped for given their petrophysic characteristics. Stimulation by acidizing was decided upon and three companies were selected to complete the program. During this program, 34 wells were acidized, which was carried out in three phases in order to diversify the methods. Of the 34 wells, 13 wells were chosen for the first phase, 13 wells for the second phase and the remaining eight wells were in the third phase. In order to study the stimulation's effects, PLTs were performed before and after each acidizing phase. The purpose of this paper is to show:The various methods of acidizing and the concentrations used in each of the three phases.Interpretations of the PLTs which enabled us to obtain flow layers, dynamic flowing pressure, static pressure, drawdown pressure and the productivity index in order to calculate the gain in production in each layer, the gain in production for each well and the flowing pressure. The combination of the PLT's results carried out on the acidized wells will be analyzed and shown in table form and graphs, which will enable us to draw a conclusion on the advantages and disadvantages of this stimulation program. Introduction Sandstone matrix stimulation has been the subject of extensive investigations for over 40 years and extensive experimental work has been conducted to investigate the reactions of various mud acid systems with damaging and formation materials(1–3). Theoretical analysis and modelling of the stimulation process have also been studied by some investigators(4–6). In this study, we wanted to share our experience of acidizing which was done in the Hassi R'Mel Field with different types of acids and various acidizing methods. The Hassi R'Mel Field is located 500 km southward from Algiers in the Algerian Sahara. It was discovered in 1956 and is one of the largest wet gas reservoirs in the world. This field has three distinct reservoir horizons: Zones A, Band C. Zone A sandstones are composed of very fine grained sandstones which are locally clay-rich with anhydritic cementing in some places. Zones B and C have very good reservoir quality with gas permeabilities ranging from 300 to 1,200 mD. Zone A also has very good reservoir quality, but its permeability is lower, at less than 300 mD. The productivity of Zones A, B and C has been reduced over time. Build-up tests performed on those wells had shown significant skin due to excessive invasion of mud used during drilling and workovers.