Using Well Testing and Production Logging Methods to Estimate Individual Frature's Parametres and Performance in a Fractured Horizontal
Authors: Grishina Ekaterina 
Published: October 2018

This paper is devoted to integrated use of well tests and well logging in horizontal MSF wells to assess the current condition and predict productivity of the wells in abnormally tight reservoirs.

To meet the this objective, we used a digital model of a horizontal MSF well that includes irregular distribution of fractures along the wellbore, differences in fracture geometries and conductivities, reservoir heterogeneities in terms of flow properties. To make calculations an Eclipse model was run with a refined space-time grid taking into consideration the task geometry.

The resulting wellbore pressure-time curves and production-rate curves for individual wells were considered as welltest inputs. All of them were interpreted using GDIS (Sapphire) software to estimate the full range of parameters that this suite allows to determine.

Then, the obtained results were reviewed in order to:

– assess the inversion efficiency subject to relation between the fracture system geometry and reservoir flow properties; – estimate individual fracture parameters and reservoir heterogeneity characteristics using a priori PLT data on the contribution of each fracture to the total well flow rate.

Welltest time may be insufficient to diagnose all the flow regimes inherent to the horizontal MSF wells. The most appropriate solution would be, therefore, to use welltest results at early times of linear and radial flow regimes.

This analysis has the advantage that at early times the fractures do not interfere between themselves. These conditions are the most convenient to determine individual parameters of each fracture. However, a priori data on the reservoir heterogeneity (openhole logging data) is needed to solve this problem, and PLT data is needed to evaluate the rate of variation of each fracture contribution to the total production (injection) volume.

The statement of this problem is the most favorable when a homogeneous reservoir is penetrated. In that case:

– welltest data within the linear flow interval allows estimating parameter which is proportional to the total surface area of all the fractures, while PLT data allows estimating the ratio between the fracture lengths. – welltest data within the pseudoradial flow interval allows estimating the reservoir flow parameters.

When the well produces from a significantly heterogeneous reservoir, one needs to know the permeability distribution along the wellbore to solve similar problems. These may be the results of estimating not the absolute values of that parameter (this problem cannot be always successfully solved from PLT data) but its relative variations.

To rapidly assess the above parameters, authors suggest approximate relationships validated by modeling results.

The obtained computational relationships differ from their analogs and were used by the authors to validate and predict horizontal MSF well productivity from the integrated welltest and well logging surveys. Modeling results allow validating the optimal technology to test and log the wells and interpret the obtained results to solve this problem.