Oil & Gas
Magnetotellurics (MT) for Oil and Gas Exploration
In the past 10 years, electromagnetic geophysical techniques have come into vogue to assist oil & gas exploration in a number of ways. These include:
- helping with interpretation of seismic data (the main data relied on in oil & gas exploration) in regions in which the data are potentially degraded. These include regions covered by high velocity rocks such as basalts and other volcanics, sedimentary sections covered by overthrusted bedrock, or host rocks covered by salt domes – all of which limit transmission of seismic signals.
- directly detecting oil and gas. Depending on the nature of contained fluids, measurements for oil and gas may be directly diagnostic of contained oil and gas.
- determining geologic structure to depth. Major and minor features may both be represented in electromagnetic data.
- mapping paleochannels. Here, paleochannels may have diagnostic characteristics such as their width and electrical contrasts with host rocks.
- mapping complex geology and other similar applications. Studies have been performed to characterize flysch and other complex geologies.
One of the primary methods in electromagnetics today is the Magnetotelluric (MT) survey which can be performed either on water or on ground. Here, we consider ground MT as a fast-paced, highly effective survey for accomplishing the oil and gas exploration tasks outlined above.
Ground MT surveys utilize a series of receivers oriented to detect transient signals related to the transmission of lightning strikes (energy source) deep within the earth. Hence, MT can record to unparalleled depths (i.e. deeper even than the 10’s of thousands of feet experienced in normal oil and gas exploration applications) although depths of investigation tend to be tailored for the geologic situation at hand.
MT receivers are deployed as a series of measuring stations along either a dedicated survey line as in seismic sections (facilitating easy comparison with seismic data) or as randomly distributed stations that can be situated to take best advantage of rugged terrain, vegetated areas or other obstacles that prohibit effective deployment of seismic arrays. Additional, near surface time domain electromagnetic (TEM) surveys may be deployed for correction of statics, and gravity / magnetic surveys may also be used to assist in structural mapping.
Typical results from Magnetotelluric surveys are resistivity images of the subsurface varying with depth and obtained through 1-D, 2-D or 3-D modeling of real-time recorded full-wave, time-series data. Rock formations, geologic structures, or oil and gas traps may potentially have unique characteristics – the objective being to map these characteristics and interpret them in combination with seismic data wherever possible. In the absence of seismic data, MT results have been used quite successfully to achieve the geologic objectives noted above.
Quantec Geoscience offers a unique combination of experience, data quality and effectiveness in targeting MT surveys to the depths required for oil and gas exploration. Experience includes more than 250 surveys conducted for mineral exploration and deep geothermal exploration with the ability to acquire oil and gas information a given based on this experience. Data quality is ensured through careful survey design and parameter selection, the longest measuring times in the industry (long measurement ensures higher accuracy of data), and proprietary processing methods. Effectiveness is a “given” with Quantec based on the results of surveys to date and the company’s focus on quality results combined with safe and efficient operating procedures.