Determination of the Optimal Wells Commissioning Rate at the Gas Condensate Field
Authors: Trifonov Artem 
Published: October 2018

Abstract
This article is devoted to the development and justification of the algorithm for selecting the optimal well input rate at gas condensate field, which allows the automatic creation of well input schedule that is characterized by the best economic performance.
A peculiarity of the gas condensate project implemented in Rospan and the other similar onshore projects is that the cost of well drilling and completion program reaches 40-50% of all investments. Synchronization of all schedules - drilling, development and construction of infrastructure for hydrocarbon treatment - is an important component of the project's effectiveness. In conditions where the consequences of geology and construction risks are commensurable, it is very important to have effective solution required to manage optimal number of wells. Preparation of wells for launching begins several years before the commissioning of the GTP, and as the process approaches this date, the pace of work is reviewed many times in order to find additional efficiency, which is primarily related to the condensate. Contractors' performance management limits the necessary flexibility and efficiency in engagement of drilling crews and construction contractors, so it is important to calculate all possible options in advance, taking into account possible uncertainties.
The problem specified in this article can be solved in several ways.
One way is to expand the existing functional of the hydrodynamic simulator, in which it becomes possible to control simultaneously two target functions (gas and gas condensate). This option is implemented due to a series of nested conditions, the number of which varies depending on the number of wells entered and the required accuracy of compliance with gas condensate production conditions. There are relevant programs written in Visual Basic for Application which allow generating the necessary fragments of the schedule (sections) in an automatic mode and integrate them into the forecast calculation schedule. This option can be implemented in case there is an understanding of which gas condensate profile is optimal. At the stage of well development design it is impossible to make a decision on the optimal gas condensate production profile without regard of economics.
With an unchanged wells stock and type of completion, the additional gas condensate production obtained with more intensive wells input (due to operation in modes with less depression) does not always compensate capital investments in the first years of the project implementation, as well as prolongation of capital investment schedule does not always compensate gas condensate production losses due to the intensification of gas wells production. Solution of this problem is specified in the second part of the article. There is a program written on the basis of Visual Basic for Application which organize and process the results of iterated calculations on determination of optimal wells commissioning rate. The user inserts basic data on deviation of well pads commissioning from "zero scenario" for each case, connects hydrodynamic model, economic model, "zero profile" of capital investments by well pads. Then, for each forecast case, the following sequence of actions is implemented in the automatic mode: the formation of the forecast case (DATA-file, SCH-file), the launch of the case in the simulator, data upload to Excel, express assessment of the capital investment profile for this schedule, calculation of economic efficiency. At the output, the user gets NPV dependence on PVI (Present value index) for a series of calculations. The extremum of this function characterizes the optimal rate of wells commissioning.
Based on the findings, examples of solving production problems are demonstrated.