Distributed wide field electromagnetic method based on high-order 2^(n) sequence pseudo random signal

To make three-dimensional electromagnetic exploration achievable,the distributed wide field electromagnetic method(WFEM)based on the high-order 2^(n) sequence pseudo-random signal is proposed and realized.In this method,only one set of high-order pseudo-random waveforms,which contains all target frequencies,is needed.Based on high-order sequence pseudo-random signal construction algorithm,the waveform can be customized according to different exploration tasks.And the receivers are independent with each other and dynamically adjust the acquisition parameters according to different requirements.A field test in the deep iron ore of Qihe−Yucheng showed that the distributed WFEM based on high-order pseudo-random signal realizes the high-efficiency acquisition of massive electromagnetic data in quite a short time.Compared with traditional controlled-source electromagnetic methods,the distributed WFEM is much more efficient.Distributed WFEM can be applied to the large scale and high-resolution exploration for deep resources and minerals.

Genetic mechanism and development of the unsteady Sarvak play of the Azadegan oil field,southwest of Iran

The upper Cretaceous Sarvak reservoir in the Azadegan oil field of southwest Iran has its oil–water contact nearly horizontal from the north to the center and dips steeply from the center to the south.The purpose of this paper is to interpret this abnormal reservoir feature by examining the accumulation elements,characteristics,and evolution based on the 3D seismic,coring,and well logging data.Generally,in the field,the Sarvak reservoir is massive and vertically heterogeneous,and impermeable interlayers are rare.The distribution of petrophysical properties is mainly dominated by the depositional paleogeomorphology and degrades from north to south laterally.The source is the lower Cretaceous Kazhdumi Formation of the eastern Dezful sag,and the seal is the muddy dense limestone of the Cenozoic Gurpi and Pebdeh Formations.Combined with the trap evolution,the accumulation evolution can be summarized as follows： the Sarvak play became a paleo-anticlinal trap in the Alpine tectonic activity after the late Cretaceous（96 Ma） and then was relatively peaceful in the later long geologic period.The Kazhdumi Formation entered in the oil window at the early Miocene（12–10 Ma） and charged the Sarvak bed,thus forming the paleo-reservoir.Impacted by the ZagrosOrogeny,the paleo-reservoir trap experienced a strong secondary deformation in the late Pliocene（4 Ma）,which shows as the paleo-trap shrank dramatically and the prelow southern area uplifted and formed a new secondary anticline trap,hence evolving to the current two structural highs with the south point（secondary trap） higher than the north（paleo-trap）.The trap deformation broke the paleoreservoir kinetic equilibrium and caused the secondary reservoir adjustment.The upper seal prevented vertical oil dissipation,and thus,the migration is mainly in interior Sarvak bed from northern paleo-reservoir to the southern secondary trap.The strong reservoir heterogeneity and the degradation trend of reservoir properties along migration path（north to south） made the reservoir readjustment extremely slow,plus the short and insufficient re-balance time,making the Sarvak form an ‘‘unsteady reservoir＇＇which is still in the readjustment process and has not reached a new balance state.The current abnormal oil–water contact versus the trap evolutionary trend indicates the secondary readjustment is still in its early stage and has only impacted part of paleo-reservoir.Consequently,not all of the reservoir is dominated by the current structure,and some parts still stay at the paleo-reservoir form.From the overview above,we suggest the following for the future development： In the northern structural high,the field development should be focused on the original paleoreservoir zone.In the southern structural high,compared with the secondary reservoir of the Sarvak with the tilted oil–water contact and huge geologic uncertainty,the lower sandstone reservoirs are more reliable and could be developed first,and then the deployment optimized of the upper Sarvak after obtaining sufficient geological data.By the hints of the similar reservoir characteristics and tectonic inheritance with Sarvak,the lower Cretaceous Fahliyancarbonate reservoir is also proved to be an unsteady reservoir with a tilted oil–water contact.

Extracting useful high-frequency information from wide-field electromagnetic data using time-domain signal reconstruction

The wide-field electromagnetic method is widely used in hydrocarbon exploration,mineral deposit detection,and geological disaster prediction.However,apparent resistivity and normalized field amplitude exceeding 2048 Hz often exhibit upward warping in data,making geophysical inversion and interpretation challenging.The cumulative error of the crystal oscillator in signal transmission and acquisition contributes to an upturned apparent resistivity curve.To address this,a high-frequency information extraction method is proposed based on time-domain signal reconstruction,which helps to record a complete current data sequence;moreover,it helps estimate the crystal oscillator error for the transmitted signal.Considering the recorded error,a received signal was corrected using a set of reconstruction algorithms.After processing,the high-frequency component of the wide-field electromagnetic data was not upturned,while accurate high-frequency information was extracted from the signal.Therefore,the proposed method helped effectively extract high-frequency components of all wide-field electromagnetic data.

The rudist buildup depositional model,reservoir architecture and development strategy of the cretaceous Sarvak formation of Southwest Iran

This paper studies the lithofacies,sedimentary facies,depositional models and reservoir architecture of the rudist-bearing Sar-3 zone of Cretaceous Sarvak in the Southwest of Iran by utilizing coring,thin section,XRD data of five coring wells and 3D seismic data.Research results include the following:According to lithofacies features and their association,the rudist-mound and tidal flat are the main microfacies in the Sar-3 depositional time.By investigating the regional tectonic setting and seismic interpretation,a depositional model was built for the Sar-3 zone,which highlights four key points:1)The distribution of the rudist-buildup is controlled by the paleo-high.2)The build-up outside of the wide colonize stage but reached the wave-base level in a short time by regression and formation uplift,and was destroyed by the high energy current,then forming the moundy allochthonous deposition after being dispersed and redeposited.3)The tidal flat develops widely in the upper Sar-3,and the deposition thickness depends on the paleo-structure.The tidal channel develops in the valley and fringe of the Paleo-structure.4)The exposure within the leaching effect by the meteoric water of the top of Sar-3 is the main controlling factor of the reservoir vertical architecture.The Sar-3 zone featured as the dualistic architecture consists of two regions:the lower is the rudist reef limestone reservoir and the upper is the tidal condense limestone interlayer.The thickness of each is controlled by the paleo-structure.The Paleo-high zone is the preferential development zone.Based on reservoir characteristics of the different zones,a targeted development strategy has been proposed.Keeping the trajectory in the middle of the oillayer in the paleo-high,and in the paleo-low,make the trajectory crossing the oil-zone and then keep it in the lower.