Method of determining the per strata reserve quality of an oil well
The present invention relates to a method of evaluating the hydraulic potential of a porous stratum defined between two depths z low and z high , the method consisting in generating periodic modulation in the rate of flow from the well, in lowering down the well and in activating for a few periods at the depth z low a measuring PLT sonde, in extracting from the resulting measurements the amplitude ΔQ low of the sinusoidal component of the flow rate modulation relating to one of the imposed periods T, the amplitude ΔP low of the sinusoidal component of the pressure modulation relating to the same period T, and the phase delay of the pressure sinewave relative to the flow rate sinewave φ low , in determining the response R low = Δ P low Δ Q low ⅇ - ⅈφ low in raising the sonde to depth z high , and in determining the complex response R high = Δ P high Δ Q low ⅇ - ⅈ φ high in calculating the complex response R stratum = R high · R low R low - R high in postulating a physical model for the stratum by numerically inverting the mathematical formula giving the theoretical complex response, in determining the hydraulic characteristics of the stratum defined by the measured response R stratum , in calculating the well productivity index IP stratum relating to the stratum in question, and in deducing therefrom the mean deposit pressure P D in the stratum using the formula: P D = P DH + Q stratum IP .
1. A method of evaluating the hydraulic potential of the section of a porous stratum that is filled with an incoming or outgoing moving effluent and that is defined by two depths respectively z low and z high , the method being characterized in that it consists:
in generating periodic modulation of the flow rate of the well;
in lowering down the well and in activating for a few periods at the fixed depth z low a sonde provided:
i) with a device for precisely determining depth, either relative to the geological series by a gamma ray detector or relative to elements of the well (CCL);
ii) with a clock; and
iii) with physical sensors suitable for measuring at least the flow of effluent in the well, the pressure, the temperature, the mean density, and the head loss gradient;
in extracting from these measurements:
i) the amplitude ΔQ low of the sinusoidal component of the flow rate modulation relative to one of the imposed periods T;
ii) the amplitude ΔP low of the sinusoidal component of the pressure modulation relative to the same period; and
iii) the phase delay of the pressure sinewave relative to the flow rate sinewave φ low ;
in determining the complex response R low to the cyclical test of period T of all of the active zones delivering effluent into the well between the bottom of the well and the depth z low , by using the formula;
R
low
=
Δ
P
low
Δ
Q
low
ⅇ
-
ⅈφ
low
in raising the sonde to depth z high , activating it for a few periods at said depth, performing new measurements, and from the new measurements, extracting:
i) the amplitude ΔQ high of the sinusoidal component of the flow rate modulation relating to the imposed period T;
ii) the amplitude ΔP high of the sinusoidal component of the pressure modulation relating to the same period T; and
iii) the phase delay of the pressure sinewave relative to the flow rate sinewave φ high ;
in determining the complex response R high of all of the active zones delivering effluent into the well between the bottom of the well and the depth z high , by using the formula:
R
high
=
Δ
P
high
Δ
Q
high
ⅇ
-
o
φ
high
in calculating the complex response R stratum of the stratum defined by the fact that the effluent it contains is delivered into the well between the depths z low and z high , by means of the formula:
R
stratum
=
R
high
·
R
low
R
low
-
R
high
in postulating a physical model for the stratum by numerically inverting the mathematical formula giving the theoretical complex response;
in determining the hydraulic characteristics of the stratum defined by the measured response R stratum ;
in calculating the well productivity index IP stratum relating to the stratum in question and in deducing therefrom the mean deposit pressure P D in the stratum, by applying the formula:
P
D
=
P
DH
+
Q
stratum
IP
given that using the sonde, and prior to activating the flow rate modulator, both the stabilized downhole pressure P DH and the net flow rate Q stratum coming from the stratum are measured.