First EAGE Workshop on Deepwater Exploration in Mexico: Foster collaboration to unlock potential

We describe a new robust solution for recovering the long-wavelength features of a velocity model with FWI. The method uses reflected and transmitted wave modes, i.e. the full wavefield, to recover high-resolution velocity models. Our new FWI gradient enables reliable velocity updates deeper than the maximum penetration depth of diving waves, hence reducing FWI's dependence on ultra-long offsets. This makes this implementation of FWI well suited for being used in reprocessing of legacy data, where long offsets are often in short supply. Results from applying the new FWI gradient to field data show that we can combine both transmitted and reflected energy in a global FWI scheme to obtain high-resolution velocity models without imprint of the reflectivity on the velocity updates. This will be illustrated with examples from the Gulf of Mexico and Brazil.

Deformation in the Campeche area of the southern Gulf of Mexico Basin was caused by tectonic events along the plate boundary between the Cocos and North American plates. The deformation history of prospects and timing of hydrocarbon migration can be understood in the context of these events in the deep water of Campeche. Multiple phases of deformation have led to the formation of fold and thrust belt structures with different styles and varying degrees of complexity.

Throughout the Tertiary, subduction of the Cocos plate underneath the North American plate, translation of the Chortis block, and indentation of the Chiapas terrane have generated distinct orogenic pulses. Two main uplift phases are associated with thin- and thick-skinned contractional deformation. These events have caused nearly perpendicular structural fabric orientations in the deepwater area of the Campeche Basin. The northern and western area of the Basin is dominated by NE-SW structures while the eastern area is dominated by NW-SE trending structures. In addition, the presence of salt in the basin has helped to control fault and fold geometries.

Onshore uplift caused by subduction of the Cocos plate together with the thermal subsidence of the Gulf of Mexico, has resulted in an overall NW tilting of the Campeche margin. This has led to the development of a large gravity slide with up-dip extension and down-dip contraction, and to shelf instability on the proximal part of the margin (in shallow water). Large-scale extensional faulting which occurs up-dip is linked to a well-developed, down-dip deep water fold and thrust belt (Catemaco FB) that is oriented NE-SW. However, the onshore Chiapanecan orogeny also caused regional contraction and not all of the outboard contraction is accommodated by the extensional basins. Gravity sliding occurs above a single extensive regional ductile detachment layer in most of the Campeche area (Louann salt), but in some areas gravity sliding has occurred along multiple, complex detachment layers.

Contractional structures in Blocks 1 and 3 show several styles that are detaching along different stratigraphic units (ductile shales or salt). These weak detachment units have different spatial distributions and partly controlled the structural style. A change in accumulated strain along the length of the Catemaco FB is thought to be due to a change in the length (i.e. areal extent) of the Louann salt detachment layer. A high degree of accumulated strain is observed in the area of shorter length of the basal detachment level and is characterized by complex structure styles and subsequent hydrocarbon migration uncertainties.

The structural complexity and deformation history in deep water Campeche and in Blocks 1 and 3 influenced trap formation as well as hydrocarbon generation timing and migration and therefore play a crucial role in the general hydrocarbon prospectivity of the basin.

Geophysical and geological surveys are carried out on either a proprietary or multi-client basis. Exclusive (also called proprietary) surveys are acquired for a single client or partnership, and their areal extend is often limited. On the other hand, Multiclient surveys are generally acquired over larger areas of potential interest with the aim to license them to several clients.

The main objective of this presentation is to show the uses of multiclient data in the offshore Mexico based on Total's experience. Some examples of the pros and cons of multiclient data will be shown, as part of the offshore exploration effort done in collaboration with other partners.

Some of the new data available are reprocessed from a pre-existing acquisition (seismic, CSEM, etc.) and some others were acquired recently in the Mexican waters (drop core, beam survey, 3D/2D seismic, etc). In some blocks, the uses of multiclient data allowed us to have a quick idea of an area and in some cases gain 18 months of time in the exploration activities plan. For the oil companies, several options are available in the market for the same kind of data. This generates a competition that had decreased the price of purchase. In Total's experiences with Mexican seismic data, in some assets the seismic price was reduced up to 70%. Another benefit of the Multiclient data is the contribution to work units for the operators of blocks (depending on the Mexican regulations). For this matter, the purchased or re-processed seismic that is located within the block could be considered as a portion of work unit under some conditions. Based on our experiences in Mexico, the uses of multi-client drop core data in collaboration with other companies has improved the petroleum system understanding of some areas with significant cost efficiency as well.

Nevertheless, for specific problems, the Multiclient data did not bring sufficient resolution and some extra reprocessing was done or will be done. Not always is it possible to reprocess the data due to a lack of complete information on the surveys. Another complexity for the uses of Multiclient data is the exchanges of information with other companies for workshops, TCM, data rooms, etc. In some cases, we were not allowed to show the data, in other cases we were not allowed to share some derivatives (depending on the contract of purchase or license of uses). Service companies were in some cases allowing the permission to show selected images with some legal terms attached to the image. We also had an example of limitation of drop core sharing that forced us to license some data just for exchange of interpretation.

In conclusion, the multiclient approach has provided an accelerated initial view of the Mexican offshore potential and it has facilitated regional work with partners. However, it has also proven technically limited when it comes to block specific work (prospects maturation, well planning, etc.) and it has exposed us to some challenges when it comes to data sharing.

Full waveform inversion (FWI) has become the preferred method for updating shallow sediment velocities. However, due to limited diving-wave penetration depth of WAZ acquisition and the geologic complexity of the region, updating subsalt velocities in the Gulf of Mexico remains challenging. Through a scheme incorporating reflection data, we extend the reach of FWI beyond diving-wave penetration depth. We present examples from the Mexican waters of the Perdido fold belt where reflection FWI successfully updates velocities at depths out of reach of diving wave-based FWI and in geologically complex situations where tomography typically struggles, including intrasalt and subsalt velocity update examples.

The crustal architecture of the central and eastern Gulf of Mexico is well imaged on modern, deep-penetrating reflection seismic data, due to thinner or absent Jurassic salt, relative to the northwestern and southern parts of the greater basin.

Within the zone of hyper-extended continental crust on both the US and Mexican margins we observe a progressive west to east transition in key tectono-stratigraphic parameters: 1) an increase in the thickness of oceanic crust from normal (7–7.5 km) to thick (> 8km); 2) increasing depth to the base-salt surface at the limit of ocean crust (with respect to the top of oceanic crust); 3) decreasing amount of salt and degree of basin-ward allochthonous transport; 4) a narrowing of the zone of hyper-extended continental crust and an increase in the dip of the continental Moho beneath the transition from hyper-extended to thinned continental crust; and 5) evidence for compression in the sediments above the base salt surface. A consistent observation along the margins is that the base salt surface is a monoclonal ramp from beneath the Mesozoic shelf edge to the oceanic crust. We do not interpret the step-up in level that occurs between the base salt and the top of the oceanic crust as a fault, but rather the marginal, constructional escarpment of oceanic emplacement.

On the thicker continental crust of the basin margins we interpret discrete domain boundaries: the northern margin of the Tampa Embayment of the central Florida margin and in a conjugate position a pronounced dextral step in the north Yucatan margin. Corrected bottom hole temperatures from wells of the Florida shelf indicate geothermal gradients north and west of the domain boundary are 30–35 Co/km, normal to high for continental crust. South and east of the domain boundary geothermal gradients range from 14–24 Co/km, anomalously low for continental crust and possibly consistent with a basement of accreted, Gondwanan, arc terranes. These observations raise the possibility that there may be important differences in crustal type, thermal structure and petroleum potential of the conjugate northwest Yucatan and north Yucatan domains.

Three of the four conjugate segments are undrilled frontier basins, where the significance of an understanding of basin evolution is most impactful for petroleum systems analysis, particularly those of the syn-kinematic and early post-kinematic Jurassic plays.

Safety, efficiency, scalability repeatability and data quality continue to drive advancements in Ocean Bottom Node (OBN) technology. Nodes are differentiated by operating depth and method of deployment and retrieval. Deepwater nodes are large, delivered to the seafloor with a high-speed loader, and subsequently transferred to a remotely operated vehicle (ROV) for deployment on a pre-planned grid designed to meet the survey's imaging objectives. In shallow water, smaller nodes are deployed to the seafloor and retrieved using an acoustically monitored passive rope.

The demand for larger, exploration style OBN surveys and the need for deepwater reservoir surveillance has led to the development of two new OBN designs. ZXPLR is a hybrid nodal system capable of dual mode deployment by passive rope in shallow water or by remotely operated vehicle in deep water. In either case, the new system improves operational efficiency, safety and flexibility while maintaining accessibility and repeatability in shallow or deep water. ZXPLR's new deployment methods combined with technologies such as blended source acquisition will allow for exploration scale OBN surveys in deep or shallow water.

ZLoF is a new type of node that extends proven OBN technology to semi-permanent reservoir monitoring in deep water (depths>500 m). Semi-permanent means the nodes are deployed once and then multiple surveys are acquired over an extended period of time. The enabling technology is a proprietary high speed underwater optical communications link, whereby, data download is performed in situ on the seafloor.

The Zama story began in July 2015 when Mexico's CNH opened the offshore basins with competitive bid rounds. Talos entered the Salinas Basin with two successful bids in the Mexico bid round 1.1, winning blocks 2 and 7. These two blocks garnered the most competitive bids and were the only blocks awarded in the bid round. Entering a new international basin poses significant challenges and operating in the Salinas Basin was no exception.

Talos was the first international operator to coordinate with CNH in developing the initial plan of exploration with new oil and gas regulations. Other challenges included logistics of getting operations equipment through customs clearance, harsh winter weather conditions with frequent port closures, and very limited infrastructure to operate the shore base. There were many geological and geophysical challenges, many common to entering an underexplored basin. These included sparse well control with limited and sometimes questionable paleo data and a well data base with location errors. Only one NAZ seismic volume which was a low frequency beam migration was delivered for bid round evaluation and contained no angle stacks or gathers. This low frequency beam migration data that lacked adequate reflector character for minibasin to minibasin correlations across fault and salt boundaries, and the 2D data provided was very poor for regional well ties away from the 3D volumes. Talos created multidisciplinary teams dedicated to the Mexico project to address the challenges and move forward with evaluation and well planning. After the contract was signed, CNH delivered additional reprocessed seismic volumes and raw gathers. The exploration team began the work of regional correlation, basin analysis, and prospect identification and mapping using the intermediate seismic volumes, working closely with consortium partners Sierra and Premiere.

Talos then launched a proprietary reprocessing project to merge surveys and process with a 45 Hz RTM output. Two primary plays were focused on. The first play was Miocene – Pliocene sandstones trapped on structural highs adjacent to and above salt. This play is DHI supported as indicated by fluid substitution modeling using local well data and proven by Pemex wells with oil pays that tie to the amplitudes. The second play was Oligocene – Cretaceous section in sub-salt three-way closures against salt. Talos focused on the shallower DHI-supported Miocene play that is similar to prolific Miocene shelf and deepwater plays in the northern GOM, where Talos has had significant success. Eight prospects were generated on Block 7, three were identified before the bid round on the older original seismic data set. Zama rose as the top prospect, with over 4000 acres of structural closure, over 400 meters of objective section, strong AVO support, a DHI with a good downdip fit to structure, and an excellent flat spot.

The operations team analyzed the operational challenges and created solutions that prepared Talos to move forward and set up our shore base at Dos Bocas. The Zama wildcat spudded May 21, 2017, drilled through the target section on July 4 and found 342 m (1,122’) gross oil pay in upper Miocene sands which were full to base. XPT gradient showed one connected hydrocarbon column with an oil gradient of 0.35psi/ft. Fluid samples yielded 29.5° API gravity and 455 GOR. The Zama well was drilled under budget and ahead of schedule with an outstanding safety record. An appraisal plan is currently being generated.

In deepwater exploration wells uncertainty in pore pressure (PP) and fracture gradient (FG) and the margin between them increases the potential risk of gas influx, lost circulation, and wellbore instability. The risk of total losses is even greater in deepwater exploration prospects that contain salt and fractured carbonates. A new managed pressure drilling (MPD) system has been used in Guyana to drill deepwater exploration wells that have many of the same problems and potential risks that will occur in Mexico.

Reservoir testing is a fundamental part of the oil and gas reservoir evaluation with impact on project economics. A conventional approach to assess reserves and producibility involves flowing the well to surface and disposing of the produced fluid. This necessitates a disposal boat and represents high costs and potential environmental concerns. Companies have been looking for alternatives to de-risk reservoir characterization while reducing times and costs associated with testing, without compromising local requirements for reserves classification.

Interval Pressure Transient Testing (IPTT), combined with downhole fluid analysis (DFA) to assess reservoir characteristics and performance layer by layer, has been the methodology of choice in Mexico.

We examine examples of IPTT acquisitions offshore Mexico, where fluid characteristics from DFA and productive potential were evaluated, and production forecasts were compared to conventional well tests. We also examine examples of use of novel Reservoir Fluid Geodynamic (RFG) studies in Exploration-Appraisal settings to resolve for reservoir architecture and de-risk future developments.