Project Report ABRIDGED VERSION

Transcription

1 Project Report N PR-HF ABRIDGED VERSION Logbaba Survey Cameroon Operated by Geodynamics Research S.r.l -Trento -Italy in November-Dicember 2009 Abridged Version Compiled in LATEX: May 5, 2010 Project N PR-HF ABRIDGED VERSION Page 1/ 13

2 Disclaimer The technical results, conclusion and recommendation contained in this report are based on the data recorded and processed by G s.r.l -Italy, with a limited amount of data provided by the client. The work was carried out according to the standard of skill and care that as expected of professionally qualified and experienced consultants. However, G s.r.l does not warrant operational decisions based on any results, conclusions or recommendation and accepts no liability for any loss, damage or costs that may be incurred or sustained though the use of the results, conclusions or recommendation of this report. The measurements were executed according to and following an acquisition design described in the Operation Manual (OM- HF-09.01) approved by G s.r.l. and the Client. Data Acquisition and data processing methods described herein are protected by the following patents: 1. European Patent Nr European Patent Nr European Patent Nr G Rovereto -TN -Italy Project N PR-HF ABRIDGED VERSION Page 2/ 13

3 Contents 1 Introduction 5 2 Target Area Existing Wells within Block Acquisition Schedule Field Quality check Seismometers Calibration Processing 7 5 Results - Overview Overview in Low Resolution Overview in Medium Resolution Overview in High Resolution Data Integration Medium- and High Resolution with Depth Structure and Satellite Overlap High Resolution Iso-Energy Image with Topographic Map Overlap 11 8 General Conclusion 12 9 References 13 Project N PR-HF ABRIDGED VERSION Page 3/ 13

4 List of Figures 1 Block 1 with the four wells and the Rig LA Measurement setup Measurement setup A-B-C with the Reference station Iso-Energy Contours map in Low Resolution Low Resolution map in 3D D Wireframe projection on the surface Significant change of Energy in correspondence with possible fault systems Iso-Energy distribution in Medium Resolution Iso-Energy distribution in High Resolution Medium and High Resolution of Iso-Energy image overlapped with a satellite view. Medium and High Resolution of Iso-Energy image overlapped with depth structure and satellite views Medium and High Resolution of Iso-Energy image overlapped with the topographic map where the shallow core holes are visible Medium and High Resolution of Iso-Energy image of Block 2 overlapped with the topographic map where the shallow core holes are visible Twinning of LA Project N PR-HF ABRIDGED VERSION Page 4/ 13

5 1 Introduction G (GeoDynamics) is a leader in passive seismic spectroscopy at low frequency, applied to detect and monitor Hydrocarbon reservoirs in exploration areas and developed fields, based on a patented technology Geospectra IPDS R (Infrasonic Passive Differential Spectroscopy). This report presents the results of an IPDS R survey conducted in the city of Douala, Cameroon, for the client Victoria Oil & Gas plc. By combining geophysical studies, well log data, depth structure data, and low-frequency passive seismic spectroscopy, the client intends to identify the new well location and find the most prominent hydrocarbon potential reservoirs within the 64 km 2 of the Logbaba Permit (PH-79) concession area, located in the eastern suburbs of Douala. The client is currently carrying out exploration drilling activity within the said permit at Ndogpassi II in Douala III sub-division. The drilling operations are aimed at confirming the presence of the natural gas reserve discovered by "Elf Serepeca" which is the former holder of the permit in the 1950 s. It is within this framework that the members of the Logbaba Association (SNH, RSM and RDL) request the operator to carry out additional geophysical studies whose results will be superposed on existing data to improve the knowledge of the Logbaba gas field and permit the identification of possible targets for future drilling operations. The entire survey, including preparation, field work and processing, was carried out by the G Srl team, according to the corporate data collection standards and equipment quality check. The Geodynamics team was locally supported by Rodeo Development Ltd (RDL) which provided, together with the contracted "Cime Service SARL", preliminarily scouting, continuous support to the Geodynamics team and assistance during data acquisition. 1. A passive seismic survey (IPDS R ) survey 2 Target Area The survey area is located in Cameroon, in the Eastern suburbs of Douala, within the client s concession block PH-79. The survey area comprises three separate blocks. Block km 2 Block km 2 Block km 2 The sum of all three areas is 28.5 km 2 and, when including the space between the blocks, the total net target area becomes 32 km 2. The dimensions of the concession area PH-79 are 8 km by 8 km or an overall area of 64 km 2. Thereby the target area represents 50% of the concession area. 2.1 Existing Wells within Block 1 The survey started with the acquisition in Block 1 [A 1 -A 2 - A 3 -A 4 ]. Block 1 comprises also four existing wells (LA-101, LA-102, LA-103 and LA-104) and drilling operations were running throughout the entire survey. The drilling took place at the Rig LA-105. ( Figure1). Project N PR-HF ABRIDGED VERSION Page 5/ 13

6 ch esea r tended the acquisition with 12 data points (Block 2). In the last phase the client called for a second extension North and Northeast and other 20 data points were added (Block3). In total 74 data points were measured and used for the processing. ics R The measurement setup designed for this survey consists of three independent mobile acquisition stations, positioned in a triangular profile, at a distance of 500 m from each other. Another separate mobile acquisition station, referred to as Reference station, was positioned in a sheltered place within the survey area (target area or acquisition area) and recorded the signal in continuous mode throughout every measurement day to acquire the specific artificial background noise of the target area. By making a time synchronization between all the seismometers within a single triangle (including the reference station), we made a particular time-based type of data analysis with all four different triangles (ABC; ABR; BCR; ACR as in ( Figure2)and ( Figure3)) within a single set-up. ynam Figure 1: Block 1 with the four wells and the Rig LA-105 According to the data provided by the client, three wells were tested over limited intervals and produced following f3 results. Individual sands produced > [10MM - 20MM] day 3 f on test per well and > 60MM day in the interval between [ ] ft during the LA-101 blowout. According to the client s data collection, all wells in the Logbaba field encountered natural gas and condensate in multiple reservoir layers. 3 eod The well tests give a reason to believe that there is a channel system of distribution of sand within the Logbaba field. Some sands are connected, others are not. Figure 2: Measurement setup Acquisition The survey was conducted by three qualified GeoDynamics team members, two geologists from the Douala-based company Cime Service SARL and six local helpers. Three vehicles were provided for the entire duration of the survey. The initial measurement program foresaw 42 data points (Block 1). During the acquisition the client requested additional measurements to the North which exproject N PR-HF ABRIDGED VERSION Each mobile acquisition station consisted of one vertical electromagnetic seismometer (GDR SM3-KV) and one digital recorder, either a 24 bit 6-channel Kinemetrics K2 ADC (Analogical Digital Converter) or a 24 bit Kinemetrics Q330 delta-sigma ADC, both with an integrated GPS unit. Each measurement point was located with a Garmin G60 GPS unit. Time synchronization between the seispage 6/ 13

7 mometers was achieved by accurate timing of the integrated GPS of the ADCs in a continuous loop modality Figure 3: Measurement setup A-B-C with the Reference station 3.1 Schedule The survey took place in the period November-December Below is a breakdown of the actual schedule. 3 days Scouting - 42 data points 1 day Mobilization and Equipment check 1 day Calibration 10 days Acquisition - 42 points 1 day Scouting - 12 additional data points 1 day Free day 3 days Acquisition - 12 additional data points 3 days Scouting - 20 additional data points 6 days Acquisition - 20 additional data points 2 days Hostile attack; Provide permit; Equipment repair 1 day Demobilization of equipment and team 32 days Total 7 days Total scouting 19 days Total acquisition 1 day Calibration 2 days Mobilization & Demobilization 1 day Free day 2 day Hostile attack; Provide permit; Equipment repair 32 days Total 3.2 Field Quality check The quality of all recordings was checked on a daily basis by the field members. During the entire data acquisition campaign, two issues have been taken into consideration. Two data point did not pass the routine daily quality check and therefore one was measured again on the following day and the other-at the end of the survey. 3.3 Seismometers Calibration A calibration setup was made on the first measurement day to check the coherence between all five seismometers, i.e. if they produce the same response when they are close to each other. All five seismometers demonstrated to be coherent within the GeoDynamics standards. 4 Processing IPDS R is predicated on the observation that a hydrocarbon reservoir s behaviour works as a filter which operates on the Seismic Background Noise (described by the Peterson model), giving a transfer function with dominant characteristics. The objective of the IPDS R approach is to process passive seismic data, using different forms of signal analysis methodology, to identify and isolate these characteristics. After applying different types of analytical methods in signal processing, the final result is an Iso-Energy Map which illustrates the distribution of the density of the Energy of the acquired signals. All Energy values, which are represented by using Iso- Enery Contours, Iso-Energy Surface maps, Wireframes and Images are quantified by means of relative units of DHI (Direct Hydrocarbon Indicator) which indicate the potential presence of Hydrocarbons within the target area and are GeoDynamics-conversional units. Project N PR-HF ABRIDGED VERSION Page 7/ 13

8 All the data was processed at the headquarters of Geo- Dynamics Research in Italy. The data received from the field crew was reviewed by the Processing department at GeoDynamics, both in the time domain and in the frequency domain, to ensure that all recordings were of satisfactory quality after the field check during the survey. One of the objectives of the passive seismic data preprocessing in the time and frequency space is to clean the signals from potential human noise, which in this case was consistent. 5 Results - Overview Three different techniques were used in separate phases with the objective to eliminate, on different levels, residual artificial noises which remained uncut at the pre-processing phase. The first overview indicates areas with high prospectivity, areas with low prospectivity and areas which in our view should be confirmed with additional measurements in the immediate surroundings. The outcome is a sequence of three Iso-Energy maps with three different levels of resolution: Low resolution; Medium Resolution and High Resolution 5.1 Overview in Low Resolution The Low Resolution map demonstrates the Energy distribution reflecting the processing results and it outlines three interesting areas within the target area ( Figure4). The first potential area is located in the lower, Southwestern, part of the target area, where Energy values are relatively high. This potential area overlaps with the Logbaba natural gas and condensate field. It is worth noting that all Energy levels, which correspond to the Hydrocarbon resonances within Logbaba and which result from GeoDynamics survey, significantly correlate to the available information from the client. Figure 4: Iso-Energy Contours map in Low Resolution The second potential area is identified in the Central - Western part of the acquisition area. By examining the distribution of the Energy contours on the Low Resolution map, and in particular by tracing significant changes of Energy levels, we propose a preliminary hypothesis about possible fault systems within the target area. Some of the proposed faults are directly visible on the surface. When changing the prospective (( Figure5) ( Figure6) and ( Figure7) ), the fault system becomes more visible and the potential areas - evident. The 3-dimensional view of the entire acquisition area with the projection of the most interesting Iso-Energy curves demonstrates significant differences between the Hydrocarbon Energy within the Logbaba field and the anomalies. Project N PR-HF ABRIDGED VERSION Page 8/ 13

9 ch esea r ics R Figure 5: Low Resolution map in 3D 5.2 Overview in Medium Resolution We increase the resolution, obtaining a more detailed result. In the Medium Resolution map the fault systems become more evident, displaying a net division between the areas, which suggests an improbable communication between these two areas (( Figure8)). eod ynam Figure 7: Significant change of Energy in correspondence with possible fault systems Figure 6: 3D Wireframe projection on the surface Project N PR-HF ABRIDGED VERSION Page 9/ 13

10 Figure 8: Iso-Energy distribution in Medium Resolution 5.3 Overview in High Resolution By applying additional processing techniques, we obtain the High Resolution map and we can zoom into the Logbaba field and the other potential areas to search for interesting details. Well LA-101 appears to match with the main fault and wells LA-102 and LA-103 are situated between two faults, at the Southern periphery of the main hydrocarbon structure. In ( Figure9) we demonstrate the outcome in High Resolution in a 3D view. Figure 9: Iso-Energy distribution in High Resolution Further increase of the resolution, bringing it to the limit of the continuity on the surface, is pointless. The High Resolution map delineates clearly the inter-related fault systems within the target area. 6 Data Integration Below we consider the Medium Resolution results to make integration with the information which GeoDynamics received from the client. The Iso-Energy maps have been overlapped with satellite maps with the objective to confirm superficial faults, locate the environment of all the potential areas and quantify the extensions. 6.1 Medium- and High Resolution with Depth Structure and Satellite Overlap Below (( Figure10)) we display the distribution of the Hydrocarbon resonance Energy values in a Medium and High Resolution images, drawn from the radial function data interpolation, to observe the fault systems along the paths where the distribution of the Energy values makes the most significant changes. We can denote that areas with a net change of color. We make an approximation of the most relevant faults within the Iso-Energy distribution map. All radical changes of Energy match possible faults, which could form Hydrocarbon compartments, as proven for the Logbaba natural gas and condensate field. Project N PR-HF ABRIDGED VERSION Page 10/ 13

11 ch esea r second and the third compartments. The structure of the density lines in the Logbaba field is well known. According to the studies, low density is detected on the left side of both the main and the secondary faults. High Resolution Iso-Energy Image with Topographic Map Overlap ics R 7 eod ynam Below (( Figure11) and ( Figure12) )we zoom into Block 1 and 2 and overlap the results with the topographic map with shallow core holes provided by the client. When matching the geographical position of these shallow core holes with the results from the passive seismic spectroscopy study only a few of these holes are situated over potential spots. The rest of the shallow holes appear to be located over nonpotential areas. Figure 10: Medium and High Resolution of Iso-Energy image overlapped with a satellite view. Medium and High Resolution of Iso-Energy image overlapped with depth structure and satellite views. In the first compartment, where LA-101 appears to be located, there is quite high density of matter. The second compartment lies beneath the wells LA102, LA-103 and the Rig LA-105. Well LA-104 is at border between the Project N PR-HF ABRIDGED VERSION Figure 11: Medium and High Resolution of Iso-Energy image overlapped with the topographic map where the shallow core holes are visible. Page 11/ 13

12 ch esea r ics R Figure 12: Medium and High Resolution of Iso-Energy image of Block 2 overlapped with the topographic map where the shallow core holes are visible. 8 General Conclusion ynam Concession block PH-79 is a very interesting block from a seismic point of view, with complex main and secondary fault systems. The cleaning of the seismic acquisitions to avoid the artificial noise mixed with the passive seismic data was difficult and sensitive work. Nevertheless the objectives of the pre- and data processing were achieved efficiently, finding a good data correlation in the Logbaba natural gas and condensate field, as well as identifying interesting potential zones. The new potential zones derive from the signals properties such as resonance signature typical for hydrocarbon reservoir. eod The presence and structure of the fault system in the Logbaba field, with its main and secondary arms, was also confirmed by the analysis of the passive seismic spectroscopy. Figure 13: Twinning of LA-101 We note that LA-105 is next to a secondary fault and a large amount of hydrocarbon accumulation could be at the convergence of the main and the secondary faults. ( Figure13) shows the possible future twinning of LA-101 (the LA-106 to be) compared with the exploration of the area in the Northeast and Southwest from Rig LA-105. The linear distance between Rig LA-105 and LA-101 is approximately m which is almost the same distance to the first lobe in the North-East. It is important to remark that any Passive Spectroscopy IPDS R survey should be used as a complementary approach to the existing exploration methods and should not be expected to produce 100% correlations with hydrocarbon accumulations. With regard to the Rig LA-105 we believe it was drilled in a good position. Project N PR-HF ABRIDGED VERSION Page 12/ 13

13 9 References Draper, N., and Smith, H. (1981), Applied Regression Analysis Scherbaum, F.(1996), Fundamentals of Digital Seismology Newland, D. E.(1981), Random vibrations, spectral & WaveLet Analiysis Oppenheim, A. V., R W. Schafer (2th Edition), Discrete- Time Signal Processing Armano, M., Vitale, S., Campagna, F.(2006), Analysis of Blue Falcon Survey Campagna, F.,(2008), Seismometers SM3-KV - Calibrations Project N PR-HF ABRIDGED VERSION Page 13/ 13