Passive Seismic Tomography dan Surface Geochemical Survey

Passive Seismic Tomography

Passive Seismic Tomography (PST) is a technique developed in the early 80s by K. Aki and students at MIT to image the subsurface of the earth. PST is similar to a CAT scan of the human body, but instead of using X-rays, we use the elastic waves generated by microearthquakes as our energy source. Microearthquakes occur anywhere in the earth where the background stress field has been perturbed even to a small degree such that data from a producing zone can be imaged from the surface using a well-designed seismic network.

PST products can be used for:

  • Define geological structures at depth

  • Locate possible hydrocarbon traps

  • Locate zones of low Vp/Vs indicating higher fluid filled regions like hydrothermal fluid (geothermal), hydrocarbon (oil and gas)

  • Reprocess 2D seismic lines for true depth

  • Lithological interpretation

Critical aspects of our PST Technique :

  • We use an Eikonal Equation solver via Finite Difference calculations – VERY IMPORTANT to use a good ray tracing modeling software in PST.

  • PST is finding best fit velocities along the ray path from earthquake to receiver, and if ray tracing is wrong, then your model will be wrong!

  • Resolution tests are very important. Can your data resolve the structures in the target area and to what detail.

ISTI‟s Finite Difference ray tracer is the best approach to modeling complex velocity environments. We are inverting for velocity by looking at sensitivity/deviations along the ray path and if that is not modeled correctly using a good method, you will miss important details. Ray paths from stations (triangles) to earthquake (red dot). Note how rays bend in center along structure caused by fault.

Benefits PST surveys are:

  • Low impact on environment, stations have small footprint.

  • Stations can be solar powered in appropriate environments.

  • Easier to deploy because less permission is needed since PST stations are cable-less.

  • Able to cover a large area in detail

  • Able to go places where conventional seismic lines cannot (e.g. Mountains, region with difficult topography, region with surface weathered limestone etc.)

  • Less expensive than 2D – 3D conventional active seismic, smaller crew and fewer station deployments.

  • Have no societal impact since source of energy is passive

  • Able identify potential seismic hazards beneath target area.

  • Energy source is stronger and beneath the network, so PST can penetrate layers which are difficult for active seismic projects.

  • Anomalous Vp/Vs targets can be discovered and highlighted by PST.

Noras Nusantara collaborate with worldwide experience seismic and software company in USA namely Instrumental Software Technologies (ISTI) to help us with the deployment and data monitoring services. All the field work will be conducted by Noras Nusantara and supervised by ISTI. Data processing and monitoring will be held in ISTI‟s office in USA. Data interpretation, geology and geophysical model will be handle by Noras Nusantara and ISTI.

Surface Geochemical Exploration

Noras Nusantara has capability to conduct Surface Geochemical Exploration (SGE) at both onshore and offshore. We collaborate with international recognized surface geochemical exploration services companies those have proven and demonstrated method to deliver valuable geochemical insight to your exploration program.

Onshore Surface Geochemical Survey
Onshore surface geochemistry is a low-cost effective method for screening large exploration areas, prospect ranking, and development drilling in order to reduce exploration risk, localize seismic survey area and validate high-grade seismic anomalies,

“Do structures contain hydrocarbons or water ?”.
The analytical results combined with other geological and geophysical data can be a guideline to determine potential area in exploration and development of petroleum resources program.

Clients repeatedly use our geochemical and geophysical methods to:

  • Evaluate large areas to determine where to acquire leases, shoot seismic or drill

  • Determine if seismic anomalies contain oil, gas or water

  • Map reservoir trends (e.g. fluvial channels) for exploration or development drilling

  • Identify by-passed or deeper production

  • Define structural trends (e.g. faults and folds) to focus exploration

We collaborate with worldwide experience geochemical survey company in USA namely Geochemical Insight to help us with the high quality analytical services. All the sample will be conducted by Noras Nusantara and shipped to Geochemical Insight for analytical services. After completion of laboratory analysis our geoscientist conduct data analysis, interpretation and reporting of result.

Services:

  • Solid-phase Microextraction Method (HSPME, C5 to C20 range)

  • Synchronous Scan Fluorescence (SSF, C6 – C24 range)

  • Acid Extractable and ICP-ES-MS analysis

  • HTTD Soil Gas Hydrocarbons (C6 – C20) by GC/MS

  • Fixed Gas (He, H2, N2, Ar, Ne, O2, CO2, CO, H2S) by GC/MicroTCD

  • Biomarker and Isotope Analysis

  • Other geochemical analysis related to hydrocarbon sources.

Offshore Surface Geochemical Survey
Marine seabed surface geochemical exploration (SGE) surveys are based on the historical observation that upward migrated petroleum from deep source rocks and reservoirs can be analytically detected in near- surface sediments and conclusions can be used to help evaluate a prospective petroleum system. The interpretation of survey results is aided by robust and consistent analytical procedures over time, resulting in a growing knowledge by the geochemists of historical and geographic background levels of the analytes in petroleum play.
Marine seabed surface geochemical exploration (SGE) surveys typically consists of a set of sequential steps, as outlined below.

  • Core Site Selection
    Seismic and/or multibeam surveys of the area of interest are used to select coring locations based on surface expression of faults, hardgrounds, mud volcanos, and other seabed features associated with upward migration of hydrocarbons.

  • Core Sample Acquisition
    USBL-navigated piston coring is used to collect the precisely located core samples. Piston coring offers several advantages over gravity coring: greater penetration depths, better core recovery, and higher quality (less disturbed) samples. Using piston coring to sample depths up to 6 meters significantly reduces intracore variability due to bioturbation, loss by diffusion of gases, and mixing of natural hydrocarbon seepage or pollution in the top meter of sea floor sediments with deeper sections of the core

  • Core Sample Screening Analysis
    Separate core section provided from every core are analyzed for headspace gases (C1-C5 plus CO2), total scanning fluorescence (measure of aromatic hydrocarbon content) and C15+Gas Chromatography (measure of aliphatic hydrocarbon content) to screen those samples for the presence of migrated thermogenic hydrocarbons.

  • Selected Sample Advance Analysis
    Selected sample candidates that show promise based on one of the screening techniques are further analyzed for saturate and aromatic biological markers as well as for the stable carbon isotopic compositions of light hydrocarbon gas components.
    These more detailed analyses can usually confirm the presence of migrated petroleum and are also often used to match hydrocarbons in the sediment extract with a specific produced oil and/or source rock, yielding information about age, maturity, depositional environment, and quality

  • Interpretation
    The end product of an SGE survey is a listing of the acquired cores that display evidence of upward migrated thermogenic hydrocarbons

Our services covering :

  • Multibeam, backscatter and water column survey

  • Piston coring, seabed sample acquisition

  • Geochemical laboratory analysis, screening analysis and advance analysis

  • Interpretation and Reporting

To perform this survey we collaborate with worldwide experience offshore Surface Geochemical Exploration company in Texas, USA namely TDI Brooks to help us with the high quality seabedcore equipment, sample handling QA/QC, laboratory analysis and reporting & interpretation. We also collaborate with local shipping and multibeam equipment provider BPPT to support the vessel for the survey.