Executive forum: New depths in exploration

Evidence of how difficult it can be to get right is found in official figures, which show exploration drilling success has been declining in recent years. Can new advances in technology help exploration teams ride a new wave of success? We asked experts Lars Johan Frigstad, Eivind berg and Pedr Solheim for their views.

Lars Johan Frigstad is President and CEO of SCAN Geophysical ASA. He has held financial positions both within the Norwegian financial markets and industrial sectors, among them six years in PGS Exploration. He is a Board Director of Clear Water 42 ASA (water purification) and has held the position as President and CEO of SCAN Geophysical since the foundation of the company in 2002.

Eivind Berg started his research career with the SINTEF Group in Trondheim. The main focus of his work was towards seismic inversion methods and their application within detailed and quantitative reservoir description. In 1997, together with a colleague, he launched seabed seismic service company SeaBed Geophysical AS in the development of the next generation of node-based technology for seabed applications. The new autonomous node technology was demonstrated on the Cantarell Field in Mexico, so far the largest 4C survey (240km2) ever executed. Berg is Technical Director at SeaBed Geophysical AS.

Peder Solheim is the Managing Director and the founder of Geograf AS. He is educated from the Agricultural University of Norway and has a Master Degree in Geodesy. He has broad experience in seismic surveying and particular in-depth knowledge within quality control and processing of seismic navigation data as well as software development related to these services.
Prior to the establishment of Geograf AS Peder has held positions such as supervisor within Geodesy and Cartography in Geco-Prakla and also later as Manager of the Seismic QC Dept. in Marest AS.

Seabed exploration is particularly challenging because surveying comprises of both seismic and sampling techniques. What key technologies are now helping to make this process more accurate and efficient compared to a few years ago?

LJF. SCAN Geophysical views ocean bottom seismic (OBS) technology as a value- added tool in addition to conventional 3D and 4D seismic services. We have developed a concept for providing customised solutions for challenging shallow water areas in between streamer coverage and land, that range from 1m to 300m water depth. We will be able to acquire both 2C and 4C data with improved quality compared with streamer seismic, but efficient acquisition in difficult areas is the main target. Obviously, our OBS concept is target-orientated and typically encompasses smaller areas compared to conventional towed streamer seismic programs. Seafloor seismic is generally more costly than towed streamer seismic but there are advantages, such as acquisition in obstructed areas, increased resolution and signal noise ratio, full wave imaging (shear waves), full wave imaging (wide imaging) and improved repeatability (4D)

2C or 4C seafloor acquisition improves resolution and is one of the most important factors in increasing the value of seismic data. Seafloor seismic offers:

• Reduced variations in spectrum content due to ghost and multiple through the use of P-Z summation technology
• Better recording of high frequencies
• Better attenuation of noise
• Better positioning of receivers
• Superior coupling
• Towed streamer records only P-waves; Seafloor acquisition records full vector waves, including shear waves.
• Better solution for gas fields

Advancements in the design of data storage and special battery packs for remote powering of seabed recording installations (‘nodes’) are making them more durable, thus increasing the amount of seismic data we can record, which in turn translates into more economical solutions when designing exploration programs. SCAN offers 2C and 4C solutions by use of Ocean Bottom Stations.

For seafloor cable acquisition, the concept developed by SCAN, is to operate a complete cable without battery packs, to avoid all the well known complications and challenges with keeping batteries operational. This new cable design provides significant reductions in size, weight and power consumption, by supplying special power from the recorder to the field equipment.

EB. Seabed exploration using multi-component or 4C (measures P pressure + vector response of compressional (P) and the shear (S) from the converted (C) waves) came along in the last decade. It was as if we were bringing land methodology to the sea floor with the shallow water acquisition as an intermediate before going to deeper water .

The methodology for recording seabed seismic data is to place the sensors on the seafloor, rather than towing them behind a vessel. Conventional steamer technology provides the benefit of very high multiplicity with a very fine sampling of the receivers along the streamer(s). In seabed exploration the lay out is different. Each sensor group or point receiver contains both hydrophones and geophones for recording of pressure (P) and the 3 orthogonal motions to get the (PP) and (PS) waves, usually called P and C waves.

The Ocean bottom cable (OBC) method has been so far the most dominant and the node methodology has gained increasingly higher interest in the market among oil companies. The limitation was the cost efficiency of having an adequate sampling of the total vector field .New trends in node applications have their basis in a unique node design based on an autonomous system where there are no cables between the units or to a surface facility. The system is based on a small, low-mass sensor package, connected to a control and data acquisition unit, which contains a processor, power supply, high accuracy clock, data storage medium and telemetry system.

With the cableless nodes, the receiver groups have a sparse geometry and the fine sampling is given by the shot density. One node can “see” the complete reservoir with a very well sampled vector field in every azimuth in increasing offset but without multiplicity. Multiplicity is then dependent on the distance between the nodes and the distance between the nodes is adjusted to the objectives. Even if progress in the last few years has come from a better cost efficiency of the operations associated with 3D modelling of the geometry, there has been a much bigger step forward in having better industry understanding of the node geometry and taking advantage of it.

What are the main risks involved in offshore exploration and what kinds of solutions are helping to minimize these?

PS. One of the main risks is rising oil prices and a conservative attitude among operators and contractors. It is a reluctance to do things in new ways. There are also too many new vessels and many new establishers in business.

LJF. Today’s market is experiencing a steady increase in demand, something that we all have been waiting years for. A significant increase in demand drives prices and profitability, with scarce availability of vessels and equipment. A period with higher profitability is necessary for a healthy industry. When suppliers make decent profits this in turn results in better equipment, which in turn helps field efficiency, which in turn promotes better end-results and/or faster turn-around. Oversupply in the market (one of the unfortunate lessons learned from the past) will revert this trend. SCAN sees this scenario as a threat to our business. However, based on current backlog in our industry, we should not experience such times for several more years. That is the reason why SCAN is in the process of releasing four additional and new seismic vessels during 2007 as we see demand for our services rising.

EB. OBS methods have the potential to solve a variety of seismic imaging problems or to reduce the main risks involved in conventional streamer operations. The acquisition of shear wave information was expected to add value but it has not yet completely lived up to its promise, primarily due to bottlenecks in processing and interpretation. Another application which has achieved increasing attention over the last few years is the use of nodes for complex imaging beneath salt pillows combined with ultra deep waters, like in the Gulf of Mexico. The full azimuth with nodes planted at depths of 2000-3000 meters may be the only methodology which can solve the problem.

Finally, there is an increasing focus on highly repeatable 4D seismic services in conjunction with EOR. Node-based 4C solutions seem to be very well suited for this due to its repeatable acoustic coupling and positioning accuracy. But there are many other reasons why nodes are particularly suited for 4D use:

• Significantly lower installation costs where no trenching/burying is needed and lower costs than for permanent buried cable installations.
• Complete flexibility in obstructed areas and easy relocation of nodes at any time in the oilfield’s life-cycle.
• Easily maintainable and fault-tolerant with no system degradation over time.
• Modular node architecture makes new system adaptations relatively easy and cost effective where the system can evolve with time without major re-investments.

How do techniques differ in acquiring multicomponent data from the seabed and what are the advantages?

LJF. With both OBS and nodes one can acquire both 2C and 4C data. However, most of the 4C data acquired so far has been processed as 2C only, due to limited 4C processing capacity and knowledge. Therefore, clients are not yet ready to fully utilize the potential improvement in data quality. SCAN will concentrate on acquisition in shallow waters and difficult areas, but will be able to offer both 2C and 4C data acquisition.

The advantages of seafloor acquisition are outlined in our answer to question one, above. Operationally, seafloor seismic is more complex when compared with towed steamer acquisition in regard to its deployment, retrieval and positioning. In SCAN’s concept, the source, cable deployment, and recording vessels are different platforms connected through wireless technology. Another solution is using radio telemetry, thus eliminating the need for an additional recording vessel. But the use of telemetric buoys with batteries is an operational challenge.

EB. In principle, there is no doubt the quality of multi-component data can be superior to that of conventional data acquired near the sea surface. It is the benefits of high multiplicity and areal density of traces, enabling advanced processing techniques that compensate for some of the limitations of surface shooting.

Node technology started with the concept of having the best possible quality data from the sea bottom. This quality concept was kept by assuring the best possible coupling of the sensor to the sea bottom. The advantage is that the planted sensor is linked by a short cable to the recording unit, maintaining the full isotopic conditions of the sensor. Optimization of the deployment by ROV(s) and only one boat are the new trend making this technology more cost effective.

How can better data results be achieved by combining seismic and other surveying techniques?

EB. Geophysical methods do play a major part in the exploration and production of hydrocarbons. Recent developments in four-component (three-component geophone and pressure) ocean bottom seismic data – including permanent sensors, 4D seismic and marine controlled source electro-magnetic (EM) data – are helpful in the mapping and production of untapped parts of the reservoir. The use of other surveying techniques in conjunction with seismic can bring important additional information, for example, passive seismic, electromagnetism and micro gravity. Controlled EM methods have been recently developed both in the time and frequency domain with all types of source configurations. Controlled source EM can, in principle, discriminate between water saturated and HC saturated reservoirs, and, in favorable conditions, identify its edge.

LJF. SCAN believes quality data from several different ‘sources’ is the only way to get the best possible end-result. Overall project turn-around time and costs normally regulate this objective, when seen from an oil company’s point of view. Recent limitation in availability of seismic equipment is an added factor that must go into oil company evaluation processes. Seeing this situation as an opportunity, SCAN is responding by providing added services beyond towed marine seismic services, such as OBS node technology.

SCAN also views seabed-logging (SBL), an electromagnetic surveying technique, as an interesting additional method of finding hydrocarbons in offshore reservoirs. Improved exploration success rates will again enhance the exploration activity and therefore the need for seismic services.

PS. Traditional marine seismic acquisition has, during the last 30 years, developed towards more and more capacity, achieved with an increased number of channels where the number of streamers and streamer length has increased.

The headword and focus has been on more power (HP). We will soon realize that the main obstacle for further improvements is accuracy, a fact already seen in 4D seismic. Our next aim is to achieve sub-meter accuracy in terms of absolute position in real-time. This is not only a question of more power (CPU-power), but a question of science. We will have to look beyond traditional techniques used in the last three decenniums. To be able to position a 20 streamer, 8000 meter long spread with a streamer separation of 12.5 meters in real-time, you will need new procedures, together with new and more advanced calculations. Compared to current acquisition systems, the new acquisition systems will look like a complex DP-system with much faster and very robust algorithms.

With the amount of raw data technology can now make available, what kind of functions should solutions comprise to offer the best tools for interpreting and utilizing captured information?

LJF. SCAN utilizes the latest field technology for recording and storing data – ultra capacity, portable and transportable HDD units are now part of this technology.

We offer onboard processing which is a value added tool to increase a project’s turn around time. In addition, more thorough analysis can be made of recorded data and its quality in the field. In addition, we can transfer ‘hand picked’ field data over satellite links to a particular client’s office anywhere in the world or to a specific onshore processing center. Again, this contributes to improved end-results and faster project turn around.

EB. Geophysics contributes to the exploration and production of hydrocarbons. Recent developments are four-component (three-component geophone and pressure) ocean bottom seismic data, including permanent sensors and marine controlled source electro-magnetic (EM) data, and 4D seismic. They have resulted in the mapping and production of untapped parts of the reservoir. Common to these developments is that the data acquisition techniques are well advanced, but processing algorithms and interpretation represent considerable added value to the petroleum industry. So far, there is a major unexploited potential for new ways of combining and using this data.

Acquisition of very high quality seabed 4C-3D data is possible and has been acquired with the node technology. Due to economic restraints, it has been generally considered up until now that seabed acquisition does not have adequate data density. This has to be slightly reconsidered. Processing and interpretation are still lagging behind to get the full benefit of already existing data. Striking images of the Cantarell field of Pemex in Mexico has been shown in the industry.They were produced using a standard state of the art processing at the time. We can imagine how much more benefits can be achieved in using more recent adaptation of node oriented algorithms in the processing. Recent tools for the interpretation of the converted waves are available. For compressional waves, OBC data is of better quality than streamer data because of better multiple attenuation, multi azimuth and high fold coverage. However, 3D OBC is still more of a multi-2D type .

Do you think there is likely to be a bigger surge in seabed exploration and seismic technology in the near future? What challenges still lie ahead?

EB. The static and dynamic characterization of petroleum reservoirs are critical for optimal production and recovery. More effective exploration methods are necessary to achieve this and we are facing the challenge of developing new geophysical breakthroughs that can identify undrained hydrocarbons in mature fields and reduce the exploration risk.

Improvement in understanding how changes in the reservoir influence seismic data is currently one of the research topics in Norway. Laboratory measurements and simulation of acoustic properties of reservoir and rocks under realistic physical conditions play an important role. The full range of reservoir properties influence the fluid flow and seismic response. Improved modeling techniques for fluid flow and wave propagation in anisotropic multi-component and multi-fluid phase solids, possibly with fractures, need to be developed. New seabed seismic and perhaps EM imaging and mapping techniques, and inversion for parameters in the reservoir, will improve data interpretation and reservoir management. 3D visualization tools provide an important technology for synergies between reservoir geology, reservoir simulation and geophysical interpretation.

PS. The requirement for pre-plot will be tighter, and the pre-plot will be a result of an operation analysis calculation, in which acquisition geometry, previous survey geometries in case of a 4D project, geology and geophysical parameters will contribute.

Geodetic, geophysical and geological scientists will in an environment of cooperation find the necessary level of accuracy, model the different parameters for an operation analysis and finally carry out a GG&G operation from pre-plot to final processed seismic data.

Fragments of such new procedures are already seen today.
AS Geograf uses geodetic and geophysical competence in connection with re-processing of historical data, in which seismic processing is used as a variable in navigation re-processing. The company also uses GIS as a tool to carry out operation analysis where geodetic, geophysical and geological parameters represent the variables. Input to GIS is typically acquisition geometry (source, streamers, feather), tide, interpreted geological horizons, and so on.

LJF. SCAN believes that there is always room for additional technologies and services in our industry, an industry that definitely is technology driven. However, it is mainly controlled by the cost factor. Expansions of OBS technology will very much depend on which areas are to be targeted for exploration by the oil company. Evaluation and development of discovered fields will always be there and is on the rise due to world’s demand for hydrocarbons. Sustained oil prices also control this, and with reasonable stability being forecasted, the OBS market should continue to grow.

Although seabed 4C technology definitely has a great future, it does pose some challenges. These include reducing acquisition costs, improving the operational field method and improving processing quality.