The Statistical Approach to Processing the Results of Gas-Well Testing: Method, Software, Analysis of Fields Data
Authors: Sukharev M.G. 
Published: December 2007

Hydrodynamical gas-well testing gives primary information for decision making during development and operation of gas fields. Existing methods used for handling of data of field measurements do not take into consideration errors of devices and of calculation model. Due to the presence of these errors it is reasonable to believe that the results of a well testing are random variables and to apply methods of mathematical statistics for their handling. Such approach opens some new aspects of interpretation of gas well testing. The methods of confluent and regression analyses were used for data handling. Computing procedures are realized by a special program which gives a possibility to handle data with the help of 14 models. The proposed procedure is applied to data of hydrodynamical testing made on wells of Urengoi field since 1985 to 1995 years. The distinguishing feature of these wells is that their flow rates are very high. The influence of errors in that case is especially significant. The considered date sample allowed to make methodical and practical conclusions.

Introduction

Results of hydrodynamic gas-well testing are very significant for a decision making at processing of gas and gas-condensate fields and planning of their development. They help to determine (1) the sizes of reservoirs (including position of gas-water contact) and their change by operation; (2) filtration and capacity parameters of productive strata; (3) physicochemical properties of hydrocarbons; (4) hydrodynamic and thermodynamic conditions in operated wellbore; (5) dynamics of phase composition of raw components in pools and wells; (6) conditions of an accumulation and lifting of a liquid and mechanical impurities from a well bottom; (7) course of corrosion processes in pipes and units; (8) technological conditions under complicated operation.

The information obtained during well testing is used for the estimation of reserves, choice of number of wells, instants of their putting into operation and assigning of production rates. So important applications of results of well testing compel to handle them with adequate, scientifically - justified methods taking into account errors of measurements. Inaccuracy of devices is especially significant for west siberian fields with very high flow rates of productive wells. Their draw-down is equal in the magnitude to accuracy rating of a pressure-gage. Existing gas-industry standards in Russia demand the use of very exact formulae to describe the fluids flow in formations and wells. The methods used for processing of results of field measurements are non-probabilistic and cannot allow for the errors of devices and models. In order to develop an adequate method of data handling the accuracy of initial information and exactitude of model must be interconnected.

Theoretical constructions must be tested by application to some real objects. As the basis for such study we choose wells of Urengoi field operated with very high flow rates. The vast data file gave a possibility to investigate the availability of different mathematical models, the stability of their parameters, the legitimacy of physical interpretation of these parameters and so on.

The statistical approach to handling of outcomes of field well testing allows to find the boundaries of applicability of known calculation techniques and the measure of reliability of the prognosis which are founded on these data.

Models: hydraulic and random parts.

We shall use models of stationary flow in a reservoir, well, reservoir - well system etc. The simplest model of flow in a reservoir is the relation between 3 variables: stratum and well bottom pressures and flow rate.