Technologies of radial drilling in the conditions of carbonate reservoirs as a way to increase oil production. From theory to large-scale pilot projects

At each stage of the field life cycle, the issues of searching for new ways of influencing the reservoir are traditionally considered in order to involve zones previously not covered by drainage, and, as a result, to increase oil recovery factor. These challenges are most relevant for fields at a late stage of development. Most of the remaining reserves are concentrated in areas with a complex geological structure, high nonuniformity of porosity and permeability and compartmentalization of the formation, which leads to a decrease or lack of coverage of reservoirs sections by drainage. The problem of remaining reserves recovery is extremely acute for fields with carbonate fractured reserves, where the operation of the reservoir pressure maintenance system is often point-like, and filtration from the matrix part of the formations is almost reduced to zero. In these conditions, radial drilling (RD) has attracted particular attention as an inexpensive and effective way to increase the coverage of reservoirs sections that were not previously involved in the development. RD refers to hydroerosive technological measures to create small channels in the formation from the wellbore, and provides additional impact on the productive formation by increasing the drainage zone and the surface efficiency vertically.

Purpose, materials and methods. The purpose of work was the search for relations between remaining recoverable reserves and the number of RD-channels, actual incremental oil rates and methods for largescale modeling of technology at the hydrodynamic model, which would make it possible to correctly assess the potential incremental oil rate for different periods of time. In this paper, a team of specialists from Gazpromneft STC LLC and Gazpromneft-Orenburg LLC proposed a method for performance evaluation of the RD technology. During the research, an analysis of the actual technological production performance of wells after RD with subsequent calculations of several cases on the hydraulic model, assuming a different number of RD-channels and their direction relative to the top and bottom of the reservoir in order to identify the optimal number of channels in the current development conditions, was made. Alternative methods of RD design as variation of the skin factor values for the predicted effectivity period of RD, the implementation of a temporary increase of the bottom-hole zone permeability and the creation of hydraulic fractures, were used.

Results and conclusion. As a result, the optimal number of RD-channels was determined, and palettes, that allow estimating the potential incremental oil rate for different periods of time in the process of modeling the hydrodynamic model, which also display the dependence of the considered variables on the remaining recoverable reserves, the number of RD-channels, were formed. Thus, the use of RD technology contributes to the best effect, which can be expressed in incremental oil rate, and can be achieved using a design that involves RD-channels, depending on the location of the horizontal wellbore in the profile cut of the oil-saturated bank. It is assumed that the approach will increase the success of the event up to 90–100 %, reducing risks of ineffective increments after the RD.

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