Study On Key Technology Of Receiver And Method For Borehole-surface Combined DERT And IP Prospecting

Oil and gas are essential non-renewable natural resources to people’s daily lives, But withthe development of society and human standard of living improves, oil and gas consumption isfast growing. A large number of domestic oilfields have entered the latter part of the mining,oil production has been unable to meet domestic demand in China, even affect national safetyand health of the economy development, therefore enhancing oil recovery is imminent. Waterinjection and hydraulic fracturing is an important approach to enhancing oil recovery, Detectionof waterflooding and fracture orientation is an important indicator of water injection andhydraulic fracturing. Electrical exploration is one of the important approach to detect hydraulicfracturing and water drive front, but in the case of weak electrical signal of deep target andenvironmental noise, existing electrical prospecting technique can no longer meet theirrequirement.For the deficiencies of the existing prospecting technology in the water injection andhydraulic fracturing exploration, tracking the latest trends of the foreign instrument, combiningthe latest development trend of domestic and foreign electrical prospecting and instrumentsystem, combined DERT and IP prospecting method is proposed in this paper. Active source isused in the method in order to enhance its anti-interference ability in oil extraction, hydraulicfracturing and other noise environment. Because of DERT is sensitive to abnormal resistivityand IP is obvious advantages to the induced polarization anomaly, more underground abnormalinformation can be got by combined the apparent chargeability and apparent differentialresistivity, which is measured by DERT and IP method respectively, in the use of data fusiontechnology. Therefore it can improve the DERT detection resolution in deep electric abnormalstructures. Then we study the technology of combined prospecting method, which its nonlinearfusion method is give out, and efficient field measurement method is designed. Throughthorough research on key technologies of front sensor and transceiver synchronization, signaldetection, borehole-surface combined DERT and IP prospecting receiving system has beendesigned and developed. This study funded by the Jilin provincial science and technologydevelopment projects “Research on Borehole-Surface Network ERT Detection System”. In theresearch of the paper I made four innovative scientific researches as follows:1. A method of apparent differential electric resistivity exploration, which was based onelectric potential gradient measurement, was put forward. According to numerical simulation, the surface electric potential anomaly and electric potential gradient anomaly were calculated.The results indicated that in the same condition, the method could achieve a better result,especially when the anomaly was in deep ground. The method provided a theory basis for thedesign of multi-channel borehole-surface combined exploration system which was based ondifferential input approach.2. A new method, which combined DERT and IP data by the way of nonlinear fusion, wasalso put forward. Based on the similarity between DERT and IP measurement, a techniquecombining the two kinds of data was studied. According to numerical simulation, electricpotential anomaly and apparent polarization electric potential were achieved. The resultsindicated that when the resistivity of the rock where water was injected or the fracturing waslocated was middle or more, surface and induced polarization electric potential anomaly weremore obvious, the direction of which was accordant to the real one. When the resistivity of rocklayer, where the anomaly was located, was low, the results were not obvious by using the twomethods respectively. However, the weak signal got from the way combined the two methods,after unequally weight sum, was anomaly obviously.3、The method of adopting L sequence pseudo random signal to hydraulic fracturingexploration in oil field was proposed. Studied the effect of L sequence pseudo random signal inborehole-surface water injection and hydraulic fracturing; desirable results can be acquired inborehole-surface detection by proper selection the clock period (t), signal length (N), andnumber of repeat cycle signal (q) of L sequence pseudo random signal. In the selection of clockperiod, in addition the power of excitation signal should ensure large enough, it also mustguarantee high accuracy in borehole-surface water injection and hydraulic fracturing systemdetection; In the selection of signal length, it should ensure cross-correlation algorithm of timedomain in a complete cycle of pseudo random signal(N t), and also ensure power spectrumbandwidth of frequency domain Far greater than the bandwidth of the system; number of repeatcycle signal should be selected as much as possible within the allowed time. And slow driftinterference, cycle interference and complex interferences can be eliminated, which avoidimpacts on borehole-surface system detection, by adjust the parameters of the pseudo-randomsignal.4. A low-noise high-resolution and multi-channel exploration system combining withDERT and IP data based on virtual instrument is developed, which uses differential input. Thedynamic range in the system gets to140dB and the short current is less than-130dB. Toachieve the function of multi-channel and large-range data receiver, a multi-channel intelligentelectrode switch device is designed. In terms of software, MATLAB and LabVIEW are usedtogether to achieve pre-treatment of weak signal, draw of parameters and Real-time imaging ofresults. The contrast and repeated experiments indicates that the system can achieve a higherresolution and a good stability.A lot of contrast experiment was done by use of multi-channel receiver system, which isdeveloped by this paper. To verify the apparent differential resistivity measurement performance of combined receiving system, contrast experiment with electrical instrumentsbased on potential method was done in Daqing Oilfield, Jilin oilfield, Liaohe Oilfield. From theresult, combined receiving system had better measuring results, and the results were verifiedby the information of drilling, in addition, it had obvious advantages in suppressing interferenceand improving the measurement. To better validate the DERT and IP data detecting accuracy,contrast experiments of oil fracturing and CBM fracturing experiment was done with microseismic measurement in Fuxian of Shaanxi province, in Jixian of Shanxi province, whichachieved similar results, and the results were more consistent with the known geological data.Compared with single DERT measurement, combined method improves the reliability of thehydraulic fracture detection results, and it shows that borehole-surface electrical methoddetecting system has higher resolution and better detecting effect in hydraulic fracturemonitoring, solved monitoring difficulties and multiple solutions of single method in low-resistivity reservoirs fractured or fracturing in deep well.