In order to efficiently asses pressure support during the field development that bears a complex structure of the void space, it is extremely important to understand how existing wells affect each other, this issue was solved at one of the fields in Tatarstan through unique cross-well surveys.

The conventional way to solve the problem of assessing reservoir connectivity consists of analysing seismic surveys, analysing the tectonics and sedimentology at focus region, conducting tracer surveys, interference tests, and production analysis. However, all of aforementioned methods display substantial deficiencies, for instance: poor seismic sensitivity towards low-amplitude faults, poor degree of detail of tectonic analysis, poor tracers representatives in complex vertical and lateral reservoir heterogeneity, if most permeable thin layer lateral anisotropy differs greatly with the main layer anisotropy, huge production losses during interference test along with receiver well shut-ins, and ambiguity in the estimation of interference with the production analysis. That's why is was decided to use pressure Pulse Code Testing (PCT) (Kamal, M. M. 1983; Ahn, S. et al. 2010; Aslanyan, A. et al. 2015; Aslanyan, A. et al. 2016) that managed to overcome those problems and avoid production deferment. The values of reservoir diffusivity and transmissibility are calculated from the recorded in revisers moment of arrival and the amplitude of the pressure disturbance from rate changes in generators. Based on the registered pressure pulse amplitudes we can estimate the influence of generator monthly injection on the pressure at receivers (Myake-shev, N. 2017). The obtained injector influence on producing well is extremely low, and indicates a poor efficiency of pressure maintains system at the tested area. That implicitly indicates on unproductive injection (Zheng, S. 2010).

In addition to a subsequent production logging it was confirmed that there is in fact a presence of a significant amount of unproductive injection due to cross flow downstairs. That was reducing the efficiency of the pressure support in the study area. This placed the start to a set of extended surveys aimed at selecting of the most appropriate injection targets of the injection wells to improve the efficiency of the pressure maintains system as well as oil production increase.

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