4D Seismic - A Technology for Future Oil and Gas Exploration

Outline of my Project What is Dimension (dot, 1D, 2D, 3D and 4D)? What is Seismic? What is 4D seismic (Time Lapse Seismic) and parameters for Time Lapse Seismic? Four basic stages in E&P life Cycle (Oil and Gas Fields) Example of Time Lapse Seismic Study Area – Norne Basin, North Sea Analysis Summary References Acknowledgement

4rth dimension here is Time and thus Dimensions X axis Y axis X axis Z axis X axis Y axis 4rth dimension here is Time and thus Time Lapse Y axis X axis Z axis

Concept of Seismic Exploration Survey ship Source of shock waves (air gun) hydrophone Sea Bed Sedimentary Rock layers Path of Reflected waves Unconformity Porous Reservoir Rock water Oil Gas Send some vibrations to the earth and listen them once they are reflected back from various reflectors i.e. record the sound waves

Air Guns Generate a Disturbance Hydrophones Detect Pressure Marine Operations Air Guns Generate a Disturbance Hydrophones Detect Pressure Land Operations Vibrators Generate a Disturbance Geophones Detect Motion Device #1 Device #2 0.0 0.3 0.4 0.5 0.6 0.7 0.8 0.1 0.2 Listening device #1 records a reflection starting at 0.4 seconds #2 records a reflection starting at 0.8 seconds Time Listening Devices 0 s  An Explosion! Energy Source .1 s .2 s .3 s Some Energy is Reflected Most Energy is Transmitted .4 s .5 s .6 s .7 s .8 s To Image the Subsurface, We Use Many Shots (explosions) and Many Receivers (listening devices) Arranged in Lines either on Land or Offshore

Seismic Data Processing of Field Record Stream SLIDE 6 Here is a display of raw seismic data – what would be recorded for one shot/explosion (marine example) The horizontal scale is receiver number which can be translated into ft/miles or meters/km The vertical scale is two-way travel time The receiver nearest the boat is on the left; receiver furthest away on the right Notice the hyperbolic shape of the reflections This is because near the boat the energy travels almost straight down and up – very little lateral distance (red arrow on right figure) For receivers far from the boat (perhaps 4 km) the energy not only has a vertical component but also a horizontal component (blue arrows on right figure) Thus the distance traveled by the blue rays is longer than the red rays – and takes more time Based on the hyperbolic shape of the reflections, we can calculate the average velocity along the ray paths Field Record Subsurface ‘Image’

Number of 2D images combined together form a 3D image 2D seismic and 3D seismic Cube 2D Images 3D Image Number of 2D images combined together form a 3D image

Time is the 4th dimension What is Time Lapse Seismic? Number of 3D seismic surveys repeated over a period of time in order to observe reservoir. Time is the 4th dimension Solution for reservoir monitoring and may act a partial substitute to the drilling Image the fluid flow in the subsurface spatially in the region not sampled by wells To monitor and predict the changes in reservoir properties as a result of production Improved understanding of drainage and helps to increase ultimate recovery rate It provides Cheap and reliable solution for reservoir monitoring and may act a partial substitute to the drilling It provides An opportunity to image the fluid flow in the subsurface spatially in the region not sampled by wells. It helps to monitor and predict the changes in reservoir properties as a result of production (Saturation and pressure changes, reservoir ambiguity, compartmentalization, undrained reserves etc.)

Principles of Time-Lapse Reservoir Imaging Base 3D seismic survey “4D” time-lapse seismic measures changes in time (changes in fluids, pressures, temperatures) Monitor 3D seismic survey

Parameters of Time lapse Study Repeatability Similarity between two seismic surveys Acquisition Geometry, Processing similarity, S/N ratio Detectability Magnitude of the seismic response to production changes Rock properties, fluid properties Interpretability Integration with available geoscience data Map based, Model based, Volume based

Why we do 4D seismic? Reduce subsurface Uncertainty - Drainage patterns Connectivity Compartmentalization Scenario choice Improved static & dynamic model - Better forecasts Better plans Improve Field performance - Better well positions (producers and injectors) Control existing wells to: increase rates/UR, Avoid water breakthrough Reduce water/gas production

Four basic stages in E&P life Cycle (Oil and Gas Fields) Exploration Appraisal Development Production Reservoir and hydrocarbon production is optimized using innovative seismic processing and interpretation techniques , thereby enhancing the value of an asset at every stage Objective changes as fields mature with a strong impact on expenditures and development and production strategies

Two Complementary 4D Analysis Techniques

Example of Time Lapse Seismic Old 3D New 3D Top Reservoir Cap Rock Oil Water-flushed Water- flushed Water OWC Oil Water Contact shifted upward OWC Repeated 2D/3D Seismic Data acquired under similar conditions at different time intervals (4rth dimension is the calendar time). The difference between two seismic vintages acquired at different time intervals give information on changes in seismic amplitude due to hydrocarbon production.

Time Lapse Seismic http://www.statoil.com/en/TechnologyInnovation/NewEnergy/Co2CaptureStorage/Pages/About.aspx

Norne Basin – North Sea Norne Field lies in blocks 6608/10 and 6608/11. 85 kilometres from Heidrun, water depth ~ 380 metres. operated by Statoil (December 1991) Located on a horst block in the south eastern part of Nordland II in the norwegian sea. Consists  of two separate  oil compartments, the Norne main structure and the North-east segment. Total hydrocarbon column is 135 m in which 110 m oil and 25m gas (Statoil, 2001). Reservoir - rocks of lower and middle Jurassic age ~ 80 percent of oil - in Ile and Tofte formations and Gas in Garn formation Reservoir depth ~ 2,500 metres below sea level.

Horst and Graben Structure of Norne basin North-East / G Segment Saddle Area C, D and E Segment Main Structure

Depth Contours laid on Tectonic Setup of Reservoir Main Structure North-East Segment

Schematic Diagram – Reservoir System Norne Garn Formation Not Formation U. And L. Ile Formation Tofte Formation Tilje Formation Gas ~ 25 m Oil ~ 110m Water

Representative Seismic Section Passing Through Wells Seismic section going through the C- and G-segment. Exploration wells – 6608/10-2, 6608/10-4, Production well – 6608/10-E-4 Injection well – 6608/10-F-4 Top Springar Fm, Top Garn Fm, Top Not Fm, Top Åre Fm. Top Garn Fm Top Not Fm Top Are Fm

Difference Seismic Section 2003 Vintage - 2001 Vintage PEAK TROUGH

Difference Seismic Section 2004 Vintage - 2001 Vintage PEAK TROUGH

Difference Seismic Section 2006 Vintage - 2001 Vintage PEAK TROUGH

Summary Measure changes in seismic response as a result of production Repeatability is a major concern Minimize changes between survey acquisition designs Baseline survey needs to be designed with 4D in mind Must integrate all information Four monitor surveys – Each adding information and value

References Vedanti, N., et al. "Time lapse (4D) seismic: Some case studies." Earth Science India 2 (2009): 230-248. Aronsen, Hans Andreas, et al. "Time will tell: New insights from time-lapse seismic data." Oilfield Review 14.2 (2002): 48-65. Aschjem, Gunnar. "Mapping Reservoir Changes Using 4D Seismic on the Norne G-segment, Norwegian Sea." (2013). Landrø, Martin. "4D Seismic." Petroleum Geoscience. Springer Berlin Heidelberg, 2015. 489-514. Osdal, B., and T. Alsos. "Norne 4D and Reservoir Management–The keys to success." 72nd EAGE Conference and Exhibition incorporating SPE EUROPEC 2010. 2010. Aarre, Victor. "Estimating 4D velocity changes and contact movement on the Norne field." 2006 SEG Annual Meeting. Society of Exploration Geophysicists, 2006. Koster, Klaas, et al. "Time-lapse seismic surveys in the North Sea and their business impact." The Leading Edge 19.3 (2000): 286-293. Landrø, Martin, et al. "The Gullfaks 4D seismic study." Petroleum Geoscience 5.3 (1999): 213-226. Landrø, Martin. "Discrimination between pressure and fluid saturation changes from time-lapse seismic data." Geophysics 66.3 (2001): 836-844.

Acknowledgement The authors would like to thank NTNU for providing Norne data. Thank you to RIL for their continuous support and guidance Thank you to IWSA for giving this platform to present our work