Second EAGE Workshop on Deepwater Exploration in Mexico: Knowledge transfer and collaboration from shelf to deepwater

Historical paleogeographic maps and sedimentary models of the Upper Miocene to Pliocene Sureste shelf margin describe middle to outer shelf, wave-dominated deltaic systems, inboard of their coeval shelf-edges and updip of significant deepwater slope reservoirs. The mechanism of sedimentary delivery from the shelf to the slope is shown to be shelf-incising submarine canyons, which tap into perched shelf deltas that do not prograde to the margin/upper slope. While a geological model of sediment delivery from the shelf to deepwater via shelf-indenting submarine canyons is sound, the absence of such canyons in the offshore seismic datasets, presence of laterally persistent train of growth-faults and linked counter-regional faults and anomalously thick deltaic deposits in offshore wells suggest that the Sureste deltas did indeed frequently make it to the shelf-edge and the paralic reservoirs in the Southeastern Basin are in fact shelf-edge delta systems, similar to sedimentary systems in the US Gulf Coast offshore Louisiana and the Orinoco prism offshore Trinidad. Amplitude extractions just below the present-day seafloor (a proxy for the last sea-level lowstand) on the Sureste margin show shore-parallel amplitudes inboard of the modern shelf edge and a distinct change to regional, shore-normal channel geometries beyond the margin. This supports the geologic model of shelf-edge delta systems nourishing a regional upper slope with turbiditic sands.

This alternative model has two main consequences: 1) significantly thickened paralic reservoirs in the Sureste shallow water, and 2) a more ubiquitous sediment delivery mechanism to the regional slope, where underlying salt withdrawal provides a structured slope onto which turbidite deposits can be ponded.

A key feature of shelf-margin deltas that is important in predicting deepwater reservoir distribution is a highly-unstable delta front to upper slope region. An interesting observation on the present-day seafloor amplitude maps in Sureste is that the observed slope channel systems do not occur directly beyond the shelf edge, but rather 5–10km further downdip. Seismic profiles in the relatively unstructured Veracruz Basin to the west show a prograding shelf-margin system with clinothems. Directly downdip of the shelf edges are highly chaotic seismic packages, interpreted as mass transport deposits (MTD's) associated with instability on the margin. These deposits are thickest on the uppermost slope and thin downdip, over a distance of 10's of km. Eventually they transition to more conformable seismic reflections, suggesting the MTD's erode much of the uppermost slope stratigraphy. This quiet zone just outboard of the shelf-edge that transitions downdip to channelized geometries in map view is also observed on the Orinoco shelf-margin. Seismic sections and piston coring of this profile confirm an upper slope, MTD-dominated setting that transitions downslope to a sandstone-prone channelized setting.

These observations on the shelf to upper slope margin offshore Sureste and resulting alternative interpretation of the depositional system and sedimentary routing significantly reduces the risk of encountering both prolific, high-quality shelf-margin paralic reservoirs inboard of the shelf edge, as well as a more uniform and regional delivery of sediments to the slope. On the slope margin, there may also exist an updip zone of MTD dominated sedimentation which merges downdip with the more desirable turbidite channel and fan systems on the structured middle slope. Sedimentary models derived from less deformed parts of the Southern Mexican margin and other analogous basins offer insights for geoscientists exploring for reservoir systems in the structurally deformed and seismically-challenged offshore Sureste basins.

With the recent opening of the deep-water provinces of the Salina Del Istmo basin in the southern Gulf of Mexico, and the availability of newly acquired wide-azimuth data, a challenging area was targeted for a pilot study to develop a deeper understanding of the geology in the Campeche deep-water region using a combination of geological and geophysical solutions, auxiliary data, and advanced technologies, including 3D basin modeling, gravity modeling, and structural restoration.

Deconvolution is routinely applied in seismic processing to enhance the resolution of migrated images. We present a deconvolution-based inverse scattering imaging condition for reverse time migration (RTM). While full multi-dimensional deconvolution is only achieved through expensive least-squares migration, we demonstrate that the 1D deconvolution imaging condition can be sufficient to provide considerable improvements to image resolution. We present a field data example that shows significant enhancement in quality of migrated images and angle gathers using 1D deconvolution imaging.

We present the main results of a Velocity Model Building (VMB) and a Prestack Depth Migration (PSDM) project in a southwestern area of the offshore Gulf of Mexico. The purpose of the project was to support the characterization of the exploration targets, the optimization of the well trajectories and the de-risking of the drilling activities by providing the highest resolution depth imaging velocities and images of the subsurface, calibrated at the three available wells.

The project was carried out by an integrated team of geophysicists, geologists and explorationists. The involvement of structural geologist is a regular procedure in such complex geological settings and was crucial for embedding salt tectonic concepts into the geophysical model. Furthermore, leveraging on the high computational capacity, several multiple salt scenarios were assessed, reducing the uncertainties in the most challenging areas: during the drilling of the first appraisal well, data were imaged with three different salt scenarios, exploiting all the available information coming from the live data from the well.

We describe two interferometry-like processes that can be used to create quasi-3D images of formation details around a well. Like with proper interferometry, the new methods allow large travel time errors accumulated over the up-to more than 50,000 ft travel path from the source to the receiver to be effectively cancelled, making the images only dependent on local velocities. In principle, the local velocities can be extracted from the data themselves, making the processes self-contained.

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During the execution of the third well from a field in Mexico's north DW, the operator was forced to design a complex coring plan to retrieve rock samples for geological characterization, log calibration & define reservoir properties, that are impossible to define by conventional means. This coring plan aimed to retrieve 330 feet of top quality sample, mainly composed by soft, unconsolidated sand, distributed in two bodies from Eocene age. Proper characterization of both targets was critical for pay zone delimitation, and not enough data was gather from previous wells. The application design includes a heavy-duty core barrel, capable to deliver 5 ¼” OD sample, a core bit with low invasion & anti whirl features, an anti-jamming system focused in reducing risk of unplanned trips. This configuration allows increasing the core barrel to 120 feet that is twice the average length used historically in the country and will reduce in half the rig cost for the whole operation.

At the well's ends, a total of 340 feet sample was catch in three runs, obtaining a 100% recovery rate. The coring job performance fulfilled the project requirements successfully and avoided a costly contingency with an estimated saving of 5 million dollars.

Zero offset Vertical Seismic Profiling (ZVSP) is a very well-known tool for time to depth calibration. This kind of geometry is specially demanded at the early stages of field development, when velocity models may still be under refinement. Borehole seismic surveys as such are usually scheduled with the wireline logs at the last section of the well, once the drilling program has already been completed. One of the questions from the ZVSP deployment is how this technology can provide decision support before the drilling is complete. Here we present a field case offshore Mexico, in the Tabasco coast shallow waters, where a ZVSP was successfully used as a geo-stopping technology in a “look-ahead” fashion, enabling the identification of an unexpected salt body ahead of the bit and a potential missing geologic formation in the sequence, which in turn allowed on-time well repositioning.

WesternGeco has been a prolific seismic player in the US GOM. Our history dating as far back as 1937 when the first marine survey started, and through 1976 when the first 3D survey was acquired. From this time to date, our understanding of salt tectonics and Deepwater exploration continues to grow. We've implemented advances in our technologies to enable the imaging of complex basins. Starting with a narrow azimuth, single-vessel mode of acquisition we grew to a full azimuth, multivessel operation. Along with our survey design, imaging techniques have also advanced to include Ref-FWI and LSRTM for better illumination beneath the salt. Model building is improved as subsurface understanding is enhanced and multidomain data increases. Finally, with the onset of OBN data we now have a new and improved reservoir perspective in the GOM. As of 2017, WesternGeco has been incorporating cloud-based technologies into its workflows to complement these advancements, such as machine learning for processing and interpretation to further accelerate our capabilities of hydrocarbon discovery.

When CNH announced the deregulation of Oil and Gas exploration in Mexico, WesternGeco took its US “Deepwater” lessons and rapidly entered the Mexico GOM with the intention of helping the government and operators accelerate hydrocarbon discovery. With our technical and financial commitments, we accomplished the equivalent of what was done in US GOM in 7 years, in less than 3 years! Our new technologies combined with gravity and magnetic acquisition provided the foundations for integrated Deepwater prospectivity evaluation. Our experience and expertise in the US GOM, combined with fit-for-purpose technology, were the fundamental success factors in accelerating exploration activities and recent discoveries in Mexico.

But it doesn't stop here, our progress continues through digital transformation. Exploration is digitally re-invented, for faster updates of play and trap models at full resolution from basin to prospect scale. All these advancements are contributing to accelerate discoveries in Mexico and will have a big impact on the development of Mexico's GOM.

Significant discoveries have been announced by foreign companies in the shallow waters of the Campeche area, Repsol and its partners have been awarded several deepwater blocks in the southern Gulf of Mexico (GoM).

One of the key challenges for explorers in the southern GoM is to derisk the economic potential of the exploration prospects using seismic amplitudes. A quantitative interpretation (QI) workflow requires the development of an interpretation framework for calibrating seismic rock properties to seismic amplitudes. Empirical observations in the context of theoretical rock physics models indicate that Miocene exploration plays are amplitude-supported.

We based our Rock Physics (RP) model on fully integrated petrophysical and petrographical interpretation of the reservoir sands and overlying shale lithology of five (5) wells in proximity of the prospect. The new predictive framework for Miocene exploration plays has been used for a confident screening and de-risking of the seismic amplitudes in terms of lithology, porosity, and fluids effects.

This paper presents the rock physics trends based on preliminary petrophysical evaluation, providing detailed mineralogical data for geophysical reservoir characterization over a specific area located in the southern part of the Gulf of Mexico (offshore).