Development of low-permeability reservoirs (less than 1 mD) is carried out with intensive flooding. Injection is performed at pressure above the formation fracturing pressure that is why in almost every well a spontaneous growth of (injection) induced fractures takes place.The main problem of pressure transient analysis in a low permeability reservoir with spontaneous fracturing is a long linear regime flow observed in the log-log plot and the absence of a basis to achieve a pseudo-radial flow. To increase the accuracy of well testing in spontaneously fractured injection wells, certain field tests were developed and run. While testing, an injection well with spontaneously induced fractures was shut-in before the bottom-hole pressure went below the fracture closing pressure, then injection resumed for a short period of time, and then the well was shut-in again to record the pressure fall-off curve. The second pressure fall-off curve shows that the pseudo-radial flow developed, because the close of the part of the fracture without proppant occurred.The paper shows field examples of interference well tests exhibiting fracture growth up to 1700 m diagnosed in injection wells. Examples of successful restriction of injection well operation and application of correlation relationships of fracture closing pressure vs. formation pressure to lower water-cut in production wells with water breakthroughs are described.

Summary Water flooding of carbonate reservoirs with complex porosity, fracture system and high vugginess is complicated by water breakthrough and quick waterflooding of the producers. At that, reservoir pressure maintenance is essential means as due to reduced reservoir energy state resulting from formation and bottom hole pressure decrease at elasto-plastic drive, well production rate decreases. Analyses of well test study show that pressure drop fracture healing takes place and leads to production loss of the producers. High vertical permeability leads to technogenic formation of gas caps at reservoir pressure drawdown below bubble point pressure and to necessity of shutting off some producers drilled under the field arch. To reduce water flooding in producers and involve non-draining uninvaded areas to injection high-elastic solutions are injected. This helps to distribute the fluid injected to uninvaded intervals. As a rule, fracture system and secondary porosity are less developed in these intervals. For that reason the reservoir are of less permeability. Liduid injection to the wells is carried out at high pressures. According to transient well test results which were undertaken before and after injection of high-elastic solutions large – spontaneous growth of vertical fracture in injection wells are observed. Thus, according to log-log plot after the undertakings logarithmic derivative view (flow pattern for single vertical fractures) is fundamentally changed. Field research results show that after the injection of high-elastic solutions and further injection at high pressure rates in reservoirs with bad flow properties artificial hydrofracs are forming which helps to involve earlier non-draining intervals.