Abstract

Area 1 is located in the Campeche Bay, offshore Gulf of Mexico at a distance from shore ranging from 2 km to 8 km and in water depths from 20 m to 40 m. Eni was awarded Area 1 in 2015, as part of the Mexico Ronda 1-Licitación 2 launched by the Comisión Nacional de Hidrocarburos (CNH). It consists of three separate blocks that include the Amoca, Miztón, and Tecoalli oil fields, previously discovered by Pemex in 2003, 2013, and 2009, respectively.

Area 1 is situated in the Sureste Basin, in the southern sector of the Gulf of Mexico, one of the most prolific hydrocarbon provinces in the world. The geology of the basin is strictly linked to the sedimentary and tectonic evolution of the whole Gulf of Mexico. The tectonic deformation of the Sureste Basin is dominated by salt movements, which started in the Upper Jurassic with a major phase in the Upper Tertiary, together with the main regional uplift events related to the Laramide (Paleogene) and Chiapanecan (Middle Miocene) orogeny. The main contribution to the hydrocarbon charge comes from the organic-rich Tithonian shale-to-marly deposits, representing the main source rock of the Gulf of Mexico. In the Sureste Basin, reservoirs are present both within Upper Jurassic–Cretaceous carbonates and in Miocene-Pliocene clastic sequences. However, in Area 1 reservoirs are limited to Tertiary clastics, because the Mesozoic carbonates are quite deep and are expected to be in unfavorable, very tight lithological facies. In general, the Tertiary clastic section could be subdivided into two mega sequences separated by the Middle Miocene unconformity. In Area 1 the most important Tertiary reservoirs are associated with the prograding, and generally coarsening-upward, platform-slope-basin turbidite and deltaic systems, overlying the Middle Miocene unconformity.

Top seals consist essentially of intraformational shale packages.

In the past 60 years, approximately 50 onshore fields have been discovered in Salina del Istmo, the westernmost part of the Sureste Basin, within the Neogene geological plays, the same where Area 1 discoveries were made, with a cumulative production of more than 2 BBOE. Starting from 2003, the exploration activity moved also to the offshore sector, where some discoveries have been made both by Pemex and by international operators, most notably the Zama discovery in 2017.

Area 1 exploration and delineation phase was characterized by several challenges, from both a geological and geophysical point of view. Three separate structures in a complex depositional and structural setting, in addition to multiple reservoirs with a wide range of oil gravity, were indeed a challenge to tackle. Legacy seismic data consisting of two different surveys, OBC and streamer, resulted in inhomogeneous seismic response with imaging issues, especially in the deeper sequences. In 2016–2017 Eni reprocessed the two surveys by merging them and producing new PSDM 3-D volumes. The in-house reprocessed volumes considerably improved the seismic imaging and allowed to build up a more reliable geological and structural model of the area. Seismic amplitudes showed up in sequences previously characterized by a poor seismic response and significantly de-risked untested plays that were the targets of the exploration campaign, opening up the prospectivity of the deeper levels of the Cinco Presidentes Formation and also of the shallower Orca 2 Formation. A rigorous use of seismic attributes and amplitude versus offset (AVO) analysis was also key in defining the exploration strategy. All the five exploration and appraisal wells were drilled in the fields’ sweet spots previously unseen on legacy seismic data and characterized by stacked amplitude anomalies mostly associated to a class III AVO response.

In the Amoca Field, the exploration and appraisal wells not only confirmed previously discovered resources but also opened up new plays in deeper stratigraphic sections or in undrilled areas. The Amoca-3DEL well encountered 358 m of net oil pay of which 206 m in new reservoirs not investigated by the Amoca-1 discovery well. All the new Amoca wells indicate the presence of an extremely efficient petroleum system, because most of the encountered sandstone reservoirs were found oil bearing.

In Miztón, a seismic amplitude and AVO-driven exploration approach also proved successful. The Miztón-2DEL well, drilled in the western sector of the structure, found 184 m net oil pay in four reservoirs, with an 80% increase compared to the total net oil pay encountered by the Mitzón-1 discovery well (102 m net oil pay).

The same approach led to positive results also in Tecoalli, where the Tecoalli-2DEL well, besides confirming the presence of the Orca 2 oil-bearing reservoir, also encountered 27 m of net oil pay in the deeper and previously undrilled Cinco Presidentes Formation.

To summarize, in 2017–2018 Eni ran a successful exploration and appraisal campaign in Area 1 drilling five exploration and appraisal wells and carrying out four production tests that resulted in a significant increase of the estimated hydrocarbon in place of the Amoca, Miztón, and Tecoalli fields. At the end of this campaign, the total hydrocarbons initially in place (HIIP) raised from the pre-bid estimate of 880 MBOE (million barrels oil equivalent) to 2.1 BBOE (billion barrels oil equivalent). Following the conclusion of the initial contractual period, Eni submitted the Area 1 Development Plan to the Comisión Nacional de Hidrocarburos that approved it on July 31, 2018. The Area 1 development drilling campaign started in the first quarter of 2019, and first oil was produced from the Miztón Field on June 30, 2019, only two-and-a-half years after the spud-in of the first exploration and appraisal well drilled by Eni.