Automated Way to Search for the Optimum Irregular Well Placement Using a Genetic Algorithm
Authors: Kazakov Kirill Viktorovich , Bravichev Kirill Arsenievich 
Published: October 2016

Oil reservoirs are characterized by varying degrees of heterogeneity filtration-capacitive properties and the distribution of oil reserves in the area. In such conditions, with sufficient certainty in the geological properties of reservoir, production of oil may be more efficient with using of irregular well placement, taking into account the heterogeneity of the reservoir. Placing well in manual mode ("by eyes") with using some maps (effective oil saturated thickness, oil deposit density and rarely others) does not guarantee that the optimal solution will be found, taking into account all important reservoir parameters and already drilled wells. The purpose of this work is the development and testing an automated approach to finding the optimal well placement.

Finding of optimum well placement was implemented as a computer program.

We used a physical analogy in which the production and injection wells are charged point particles of two types in the plane. Stratum is represented as a two-dimensional map of the potential, and for each of its cells numerical value (potential) of the feasibility of placing well in it is calculated. This potential depends on the properties of the reservoir and the distance to other wells. An objective function is used to evaluate the optimality of a particular arrangement. It has a maximum at a maximum distance of each well from all others, a uniform distribution of production and injection wells, placing production wells in the area of influence of injection wells, and placing wells at most favorable location of the reservoir.

Search of a well placement which gives the maximum value of the objective function is performed using a genetic algorithm. To this some random initial well placements are generated. Each initial placement creates a number of descendants. The descendants are created by random changes (mutations) of coordinate of random number of wells, and random exchanges of wells type (from production to injetion and from injection to production). A descendant with the maximum value of the objective function creates new offspring. Evolution can last a specified number of generations.

The effectiveness of the proposed approach for placing of wells was evaluated in several test cases. In each case we considered two variant of placement the same number of wells: regular and irregular placement by the genetic algorithm.

Dynamic of oil production for considered variants were calculated by 3D numerical simulation. The calculation results showed that the proposed approach for getting of optimal well placement can give more values of oil rates and cumulative oil production. However, the evaluation of the objective function requires setting of weighs of parameters through which it is expressed. The correct choice of these weights substantially defines development effectiveness of given irregular grid.

The paper developed an approach for the automatic irregular placing of of wells, allowing to take into account complex of basic geological and technological parameters affecting the efficiency of the development. The proposed approach has been implemented in a computer program and can be used in the presence of geological and hydrodynamic models of the reservoir. Using of the proposed approach can achieve, with an appropriate choice of input settings, higher oil recovery and higher oil rates in comparison with the development based on regular placing of wells.