A METHOD FOR MONITORING A HIGH-RESISTIVITY RESERVOIR ROCK FORMATION

摘要

A method for monitoring a high-resistivity reservoir rock formation (2) belowone or more less resistive formations (3), comprising the following steps:Transmitting an electromagnetic signal (S) propagating from near a seafloor orland surface (1) by means of an electromagnetic transmitter (5) powered by avoltage signal generator (G). The electromagnetic signal (S) propagates fromthe seafloor (1) and is guided along a conductive string (7) to the high-resistive formation (2), and propagates as a guided-wave electromagneticsignal (S2) at a relatively higher speed (V2) inside the high-resistivityformation (2) than a propagation speed (V3) in the less resistive formations(3). The guided-wave electromagnetic signal (S2) gives rise to an upwardrefracting electromagnetic signal (R3) having the relatively lower propagationspeed (V3) in the less resistive formations (3) and having an exit anglenearer to the normal N to the interface between said high-resistivityformation (2) and the lower-resistivity formation (3), and gives rise to asteeply rising refraction wave front (F3). The refracted electromagnetic wavefront (F3) comprising refracted electromagnetic signals (R3) is detected alongan array of sensor antennas (6a, 6b, 6c, ..., 6k, ..., 6n) along the seafloor,the array having a direction away from the transmitter (5). In a preferredembodiment of the invention, the electromagnetic transmitter (5) comprises anantenna (50) transmitting the electromagnetic signal (S) to an upper end (70U) of an electrically conductive string (7), e.g. a steel casing or liner, theupper end (70 U) being arranged near said seafloor (1).