SUBSTANTIATION OF SELECTION OF DRILLING MUD TYPE FOR INITIAL OPENING OF KHAMAKINSKY HORIZON TERRIGENOUS RESERVOIR

Abstract

Most of the explored and estimated oil reserves of the East Siberian oil and gas province are located in the Republic of Sakha (Yakutia), and in particular, the field is located on the territory of the Lensky district, the development object of which is the formation of the Hamakinsky horizon. The reservoir is characterized by high reservoir properties, oil-saturated thickness, medium permeability, abnormally low pressures, low temperature, the presence of carbonate, terrigenous, chemogenic and karst rocks in the geological section, tectonic deformations, reservoir intrusions and salt-saturated interlayers. These factors create problems in the process of its initial opening, and during further operation cause the deterioration of its filtration and capacitance properties compared to those stated in the design documentation. The use of highly mineralized or anhydrous drilling fluids recommended for drilling wells in the considered oil and gas zone does not allow to overcome the instability of rheological properties, an increase in the values of the filtration index, deep clogging of the reservoir, the accumulation of fluid density and the risk of high repression on the reservoir. The article theoretically substantiates the expediency of using invertemulsion solutions (IES) for the initial opening, the effectiveness of which, compared with aqueous solutions, is expressed in the exclusion of the formation of sludge crusts, stable formation oil-water emulsions and swelling of anhydrite, and the reduction of clogging effect in the near-wellbore part collector. Nevertheless, in order to justify the introduction of one or another composition (type) of IES at the stage of theoretical research, various compositions based on mineral oil, diesel fuel, oil obtained in the course of earlier laboratory tests were considered for comparison with water-based solutions, taking into account required density and clogging action of the flushing fluid, physical and chemical inertness of the dispersed phase of the solution, low formation temperature. The substantiation of the most effective type of fluid was carried out using a methodology based on the method of analysis of hierarchies, the optimality criterion in which is the largest weighted average value of the superiority (priority) of one of the drilling fluid options over others simultaneously in all parameters, taking into account the degree of importance of the latter. Based on estimates of normalized and ideal priorities, it has been established that its highest value, both in the case of a distributed synthesis method and in the ideal one, belongs to oilbased IES.