TenzorGEO provide cutting-edge and cost-effective seismic technologies which enhance the productivity of exploration and development of oil & gas fields. In that scope, some extended passive seismic technologies, comprising a number of different, yet complementary techniques that are encapsulated through the collaborative research between the industy and academia are presented here.
It is a DHI (Direct Hydrocarbon Indicator) methodology that is easily applicable, cost-effective, environmentally friendly and a robust alternative to find untapped oil-gas deposits from matured or brown fields. In addition, it can be implemented in situations, where conventional practices would not be an option, either due to block size, active seismic waves energy penetration issues, budget limitations, accessibility and/or environmental restrictions. LFS has already been applied extensively to several geological and geographical situations in Russia, Ecuador and India, wherein the success ratio in finding additional hydrocarbons is about 86%. All three wells confirmed our forecast on pilot project In Gandhar Field of Cambay Basin in India. In other words, it defines productive and non-productive zones at reservoir-scale of under-developed, developed and matured fields within the limited-time and budget.
LFS utilizes natural sources of low-frequency 1-6 Hz vertically oriented P-waves. An accumulated pre-processed spectrum of the ambient microseismic signal is considered as the result of filtering by the geological media i.e. amplitude-frequency curve (AFC) of media. Due to the mechanics of fluid-saturated, fractured and porous media, oil and gas reservoirs have a high dispersion of velocity and high attenuation at low frequencies. A thin layer of oil/gas reservoir with high attenuation amply reflects the low-frequency P-waves that is why it transforms AFC of the media under observation point on the ground surface.
The advantages include: (a) mobility (conducting of operations in regions difficult to access); (b) efficiency (surveys in an area of 30 km2, with 300-400 measurement points, can be processed in two months’ time i.e. 1 month for data acquisition and 1 month for processing, interpretation and delivery of a report); (c) ecological cleanliness (without explosives, chemicals and drilling). Over 160 projects are completed with a cumulative area amounting to more than 3200 km2. The client list includes Gazprom, Rosneft, LUKOIL, TATNEFT, Gazpromneft of Russia, Grupo Synergy E&P of Ecuador and ONGC of India.
It is a passive microseismic monitoring technology that facilitates better reservoir management and improvisation of hydrocarbon recovery. The technique is based on the idea of deriving vital additional information about a reservoir by recording and processing microseismic events that occur throughout the production life of hydrocarbon reservoirs. These microseismic events have their origin from natural (opening and closing reservoir cracks as a result of deformations within the earth's crust) and man-made (hydraulic fracturing and injecting liquid into the reservoir) factors.
The locations of these microtremors inside the reservoir will provide insight into the behaviour of the reservoir over a period of time and will also provide the necessary information for the interpretation of reservoir activity, fracture network characterization, and fluid flow paths. The microseismic observations of the reservoir permit to draw conclusions on the behaviour of the reservoir, as follows:
Active fracture/faults: Since microseismic events occur mostly on pre-existing fractures or faults, the computation of their location provides a way of delineating active faults. It is, therefore, possible to obtain the geometry and position of these faults and to determine the active fault network in the reservoir, from a sufficient number of microseismic events recorded over a long period of time.
Hydraulic fracture monitoring: The microseismic events originated from hydraulic fracturing (horizontal well bores) denote not only their location, but also the seismic moment sensor that permits identification of the directions of fracture propagation.
Fluid-front movement: The injection of gas and water during production or during hydrofracturing operations induces high fluid pore pressure changes at the fluid front, triggering microseismic events. By examining the change in the location of these events in time, a picture of the fluid-front movement inside the rock mass can be achieved. Furthermore, the microseismic data will give very useful information about the preferred flow paths and will indicate possible flow anisotropy.
Identification of anomalous objects in geological media: This permits to improve the safety and efficiency of drilling, workover operations, well abandonment and subsequent monitoring of abandoned wells.
As this technology is performed from the surface without any disturbance to the ongoing operations in the neighbouring wells, no additional costs incurred to the clients (significantly cheaper in total costs). The other benefits include: (a) best signal-to-noise ratio as the events are recorded by highly sensitive 3-component wideband wireless seismometers; (b) 3D full-wave numerical simulation permits application of all types of waves: compression, shear, exchange, and re-reflected waves; (c) maximum likelihood method that is operated on full wave form, permits the events’ localization at low signal-to-noise ratios (the most noise-immune method); (d) as the tensor of the seismic moment is calculated for each seismic event, the type of event and the orientation of the crack that formed the event are easily determined.