4D Seismic Reservoir Monitoring Research Articles

A large-scale validation of OBN technology for time-lapse studies through a pilot test, deep offshore Angola

In early phases of offshore field development, repeated marine seismic surveys recorded with towed streamers have been successfully processed to image changes in reservoir fluids through time and hence have contributed to important reservoir development decisions such as elaborating future production and injection plans. In such cases, the negative impact of surface or underwater obstacles on the final image has been mitigated using undershooting strategies. Nevertheless, even in the most favorable cases, this has been achieved at the expense of 4D repeatability because short-offset illumination is missing in the undershoot survey and the azimuthal distribution within the offset classes becomes inconsistent with the base streamer data. As the field development proceeds, especially in deep offshore contexts, a complex network of in-sea and subsea installations is progressively put in place and the Health, Safety, and Environmental (HSE) issues related to seismic vessels or recording cables coming close to production facilities can no longer be neglected, making the conventional streamer or OBC acquisitions challenging, or simply not feasible. As a result, industry is proposing a “sea-floor receiver” solution with ocean-bottom nodes (OBN) for imaging and monitoring reservoir production below infrastructures. OBN are autonomous seismic recording systems deployed on the seafloor with remotely operated vehicles (ROVs). Previous tests and studies (Boelle et al., 2005; Ceragioli et al., 2006) have shown that OBN technology may be appropriate for reservoir monitoring. Here we present the results of the first large-scale OBN project completed by Total E&P Angola, between September 2008 and April 2009, over the deep-water Dalia Field, Block 17, with the aim of validating the use of this technology for 4D seismic reservoir monitoring.

Using influence diagrams to analyze decisions in 4D seismic reservoir monitoring

Exploration and production decisions are complex due to several uncertainties: uncertainty in the geologic properties, seismic imaging, repeatability, reservoir structure, rock and fluid properties, etc. Furthermore, several decisions need to be made over the entire life cycle, and often it is not clear how current decisions might affect the future bottom line. In the exploration and characterization stage, more information is acquired about the reservoir structure, reservoir rock and fluid properties, and the spatial distributions of lithology, porosity, and saturations. Exactly how much information needs to be acquired is a critical decision at this stage. Later, decisions have to be made about the technical and economic feasibility of seismically monitoring the reservoir during production. Simple tools like decision trees have become popular (e.g., Newendorp and Schuyler, 2000) but complex situations demand the use of more sophisticated decision-analysis tools and their integration with the existing to...

Business and technology challenges for 4D seismic reservoir monitoring

4D seismic reservoir monitoring is a relatively new technology that consists of repeating 3D seismic surveys in order to make time-lapse images of the fluid and pressure fronts as they move in a subsurface reservoir during hydrocarbon production. When successful, 4D seismic can locate areas of bypassed oil for new drilling opportunities, map out water-flooded areas to avoid the costly mistake of drilling new wells into swept zones, and identify the geometry and nature of reservoir flow compartments that are key to optimizing hydrocarbon recovery. 4D seismic has evolved during the past decade from a series of geophysical field experiments to a practical reservoir monitoring tool that can add significant value to the reservoir management process. However, it has not yet become a mainstream technology. In this article I will discuss some of the business and technology challenges that need to be addressed before 4D seismic can become as widely utilized in the petroleum industry as 3D seismic is today. Figure 1 shows the geographical areas of the world where most of the industry's 4D seismic activity is located today. Figure 2 shows the cumulative 4D seismic expenditures to contractor and service companies, for the four years 2000–2003 inclusive. Of a total (US)$500 million cumulative 4D service expenditures, about $400 million (80%) has been spent in the North Sea, $35 million (7%) in West Africa, $30 million (6%) in North America, $20 million (4%) in the Far East, and $15 million (3%) elsewhere. This estimate of expenditures is for 4D seismic acquisition, processing, and interpretation/analysis services, as determined by a recent study we participated in at the French Institute of Petroleum. Figure 1. Geographical distribution of current 4D seismic activity. Figure 2. Cumulative expenditures on 4D seismic services to contractor and service companies for 2000-2003. Of $500 million cumulative 4D service expenditures, about $400 …

Assessing the Feasibility of 4D-Seismic Reservoir Monitoring

This article is a synopsis of paper SPE 50666, "Assessing the Feasibility of a 4D-Seismic-Reservoir-Monitoring Project," by B. Blonk and R.W. Calvert, Shell Intl. E&P B.V.; J.K. Koster, Norske Shell A/S; and G. van der Zee, Shell U.K. Ltd., originally presented at the 1998 SPE European Petroleum Conference, The Hague, The Netherlands, 20-22 October.

Practical Issues of 4D Seismic Reservoir Monitoring: What an Engineer Needs to Know

Summary Time-lapse three-dimensional (3D) seismic, which geophysicists often abbreviate to four-dimensional (4D) seismic, has the ability to image fluid flow in the interwell volume by repeating a series of 3D seismic surveys over time. Four-dimensional seismic shows great potential in reservoir monitoring and management for mapping bypassed oil, monitoring fluid contacts and injection fronts, identifying pressure compartmentalization, and characterizing the fluid-flow properties of faults. However, many practical issues can complicate the simple underlying concept of a 4D project. We address these practical issues from the perspective of a reservoir engineer on an asset team by asking a series of practical questions and discussing them with examples from several of Chevron's ongoing 4D projects. We discuss feasibility tests, technical risks, and the cost of doing 4D seismic. A 4D project must pass three critical tests to be successful in a particular reservoir: Is the reservoir rock highly compressible and porous? Is there a large compressibility contrast and sufficient saturation changes over time between the monitored fluids? and Is it possible to obtain high-quality 3D seismic data in the area with clear reservoir images and highly repeatable seismic acquisition? The risks associated with a 4D seismic project include false anomalies caused by artifacts of time-lapse seismic acquisition and processing and the ambiguity of seismic interpretation in trying to relate time-lapse changes in seismic data to changes in saturation, pressure, temperature, or rock properties. The cost of4D seismic can be viewed as a surcharge on anticipated well work and expressed as a cost ratio (seismic/wells), which our analysis shows ranges from 5 to 35% on land, 10 to 50% on marine shelf properties, and 5 to 10% in deepwater fields. Four-dimensional seismic is an emerging technology that holds great promise for reservoir management applications, but the significant practical issues involved can make or break any 4D project and need to be carefully considered.

Abstract: 4D Seismic Reservoir Monitoring: What is the Role of Geology?

Abstract: 4D Seismic Reservoir Monitoring: What is the Role of Geology?

4D seismic pressure-saturation inversion at Gullfaks field, Norway

David Lumley, Don Adams, Mark Meadows, Steve Cole and Ray Ergas* of 4th Wave Imaging, a Californian company specializing in advanced 4D seismic software development, describe its application of proprietary pressure-saturation inversion to the Statoil operated Gullfaks field, offshore Norway. Time-lapse 4D seismic reservoir monitoring is experiencing rapid acceptance as a practical reservoir management tool, as evidenced by three full days of technical presentations on the topic at the recent June 2003 EAGE Conference in Stavanger, Norway. The 4D seismic technique is useful to help map bypassed oil, monitor costly injection programs, and improve our understanding of reservoir compartmentalization and the fluidflow properties of faults. Most of the applications to date have tended to be qualitative rather than quantitative. For example, 4D seismic practitioners often examine time-lapse seismic amplitude maps and develop a qualitative interpretation of where they think fluids are flowing in the reservoir, constrained by supporting data such as geologic control, well logs and engineering production information. However, there is a growing desire to obtain more quantitative results from 4D seismic data, for example, the ability to create pressure and saturation maps or volumes with calibrated physical units of saturation and pressure to assist engineering workflows and reservoir management decisions. This paper presents a case study in which we apply quantitative Pressure-Saturation Inversion (PSI) technology developed by 4th Wave Imaging to the 4D seismic project at the Gullfaks field, offshore Norway.