Concentrating seismic energy in a selected target point in an underground formation

A method of providing at least one focused waveform-controllable seismic source to enable concentrating seismic energy in a selected target point in an underground formation, which method comprises the steps of:

• (a) performing a seismic survey of the underground formation using the at least one waveform-controllable source i, and a set of downhole seismic receivers j, and recording the signals uij(t), wherein each source is activated by a signal si(t);
• (b) selecting a downhole seismic receiver k from the set of seismic receivers to be the target point;
• (c) taking the direct part udik(t) of the signal uik(t) and making an inverse filter (udik(t))−1 of the direct part of the signal;
• (d) selecting a desired waveform fk(t−t0) to be focused at the location of the downhole seismic receiver k at time t=t0;
• and
• (e) calculating the new signal with which the seismic source i is to be activated in accordance with snewi(t)=si(t)(udik(t))−1fk(t−t0) to get a focused source i of which the waves arrive at the downhole seismic receiver k with the desired waveform fk(t) starting at time is t0.

A method of providing at least one focused waveform-controllable seismic source to enable concentrating seismic energy in a selected target point in an underground formation, which method comprises the steps of:

• (a) performing a seismic survey of the underground formation using the at least one waveform-controllable source i, and a set of downhole seismic receivers j, and recording the signals uij(t), wherein each source is activated by a signal si(t);
• (b) selecting a position 1 to be the target point, wherein the position 1 is near a downhole seismic receiver k of the set of seismic receivers, and determining from the signals uij(t) the one-way travel times τik from a number of sources i to the seismic receiver k near the target point at the location 1;
• (c) taking the direct part udik(t) of the signal uik(t) and making an inverse filter (udik(t))−1 of the direct part of the signal;
• (d) selecting a desired waveform fk(t−t0) to be focused at the location of the downhole seismic receiver k at time t=t0;
• and
• (e) calculating the new signal with which the seismic source i is to be activated in accordance with snewi(t)=si(t)(udik(t))−1fk(t−t0) to get a focused source i of which the waves arrive at the downhole seismic receiver k with the desired wave form fk(t) starting at time is t0, and applying a correction on the signal with which the seismic source i is activated, wherein the correction is given by Δtcorri=τik−τi1, τi1 being the estimated one-way travel time from source i to the target point 1, such that snewci(t)=snewi(t−Δcorrti).

A method for focusing seismic energy generated by an array of impulsive seismic sources to a target point in an underground formation, the steps comprising:

• (a) performing a seismic survey of the underground formation by generating seismic energy utilizing a set of impulsive seismic sources i and receiving said seismic energy utilizing a set of downhole seismic receivers j, and generating and recording signals uij(t);
• (b) selecting a position k as a target point;
• (c) determining from signals uij(t) one-way travel times τik from said sources i to said target point;
• (d) calculating ti=t0−τik to obtain activating times ti at which impulsive seismic sources i have to be activated, in order focus seismic energy generated by said seismic sources i to arrive at said target point in phase at time t0;
• and
• (e) activating said array of seismic sources according to activation times ti and receiving and recording signals uik(t) at said seismic receiver k.

A method for focusing seismic energy generated by at least one waveform-controllable seismic source at a selected target point in an underground formation, the steps comprising:

• (a) performing a seismic survey of the underground formation by generating seismic energy utilizing at least one waveform-controllable source i, and a set of downhole seismic receivers j, and recording the signals uij(t), wherein each source is activated by a signal si(t);
• (b) selecting a downhole seismic receiver k from the set of seismic receivers to be the target point;
• (c) taking the direct part udik(t) of the signal uik(t) and making an inverse filter (udik(t))−1 of the direct part of the signal;
• (d) selecting a desired waveform fk(t−t0) to be focused at the location of the downhole seismic receiver k at time t=t0;
• (e) calculating the new signal with which the seismic source i is to be activated in accordance with snewi(t)=si(t)(udik(t))1 −fk(t−t0) to get a focused source i of which the waves arrive at the downhole seismic receiver k with the desired waveform fk(t) starting at time is t0;
• (f) activating said at least one seismic source i in accordance with activation time snewi(t)=si(t)(udik(t))−1fk(t−t0) and receiving and recording signals uik(t) at said seismic receiver k.