GEO ExPro

Beneath Belize

New online data repository with all seismic acquired since the late 1960s
This article appeared in Vol. 14, No. 1 - 2017

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A new online national data repository for Belize provides access to a digital catalog of all seismic data acquired across the country since the late 1960s – hitherto tucked away in dusty corners of the Geology and Petroleum Department in the country’s capital, Belmopan.

The Yucatan Peninsula is a distinctive landmark – a predominantly limestone-based platform that separates the Gulf of Mexico from the Caribbean Sea, and is perhaps best known for its holiday resorts, Mayan history, and of course the Chicxulub impact crater. Situated mostly inside Mexico’s territorial borders, it is bounded to the west by the prolific Sureste Basin and the oil and gas deposits of the Reforma- Akal and Macuspana provinces, fields that contain combined proven reserves of over 12.5 Bbo. 

Farther south, the peninsula extends into Englishspeaking Belize, which is nestled in the crook of the eastern Caribbean coast between Mexico and Guatemala. What of its hydrocarbon prospects? Considerable attention has been focused on Mexico’s energy sector over the past two years since the launching of a series of new bid rounds that, for the first time since the 1930s, have opened the path to foreign investment. Could the recent enthusiasm for exploration in the region rub off onto other parts of Central America? 

  • Map showing the location of Belize in context with the major structural elements of the region. Adapted from USGS Open File Report 97-470-K.

Oil Revitalized Economy 

A photo taken from the GPD offices in the center of Belmopan, overlooking the main market square. (Source: Gareth Williams) Formerly British Honduras, Belize achieved independence as a parliamentary democracy from the United Kingdom in 1981, although the country, like other former English colonies of the Caribbean, retains Queen Elizabeth II as its titular head of state and it is a member of the British Commonwealth of Nations. 

Measuring 22,810 km2 (slightly bigger than New Jersey or Wales), Belize has a population count of around 368,000, a number made up of seven recognized discrete ethnicities; these are the Maya, Mestizo, Creole, Garifuna (African-Amerindians), East Indians, Sino-Asian/Chinese, and German-Mennonites. 

Belmopan has been the capital of the country since 1970. It is the smallest national capital in the continental Americas with a population of around 16,500, and was built inland as a planned community following the near-destruction of Belize City, its former capital situated on the coast, by Hurricane Hattie in 1961. Belmopan is the seat of the government and it is here that the Geology and Petroleum Department (GPD), the body that looks after all aspects of exploration and production activities in Belize, is located. 

The ancient Mayan site of Xunantunich, looking westwards across dense jungle covering of the Corozal Basin in the background. (Source: 123rf/lanabyko) Prior to 2006, Belize’s economy was primarily dependent on traditional exports such as sugar, citrus, bananas, timber and fish products, together with the inflow of money that comes with foreign real estate investment and tourism. The latter are a result of the attraction of the country’s Caribbean coastline and several island resorts (‘Cayes’) that lie in waters sheltered by the Mesoamerican Barrier Reef system, the second longest in the world. 

Then in 2005, after nearly 50 years of failed exploration, commercial quantities of oil were finally discovered by the Mike Usher-1 well, drilled around 25 km due west of Belmopan in the small Mennonite community called Spanish Lookout (after which the field was eventually named). Production from here would soon catapult oil into the category of primary revenue generator for Belize, and trigger renewed optimism for its exploration prospects. 

Geology and Exploration History 

Located just north of the broadly east-west trending Montagua-Polochic fault system that forms the boundary between the North American and Caribbean plates, the overall geological setting of Belize can be sub-divided into three entities: the Corozal Basin in the north, and the Belize Basin in the south, separated by the Maya Mountains. These mountains rise up in places to over 900m and are comprised of Permo-Carboniferous metasediments and volcanics with Upper Silurian and Triassic igneous intrusives, and represent a faulted block of Mayan crust that tilts westward towards Guatemala. This fault trend continues into Guatemala, where it is expressed as the La Libertad Arch, partitioning the intracratonic Peten Basin into north and south sub-basins. The Belize Basin, which borders the Maya block to the south and extends offshore, is essentially a continuation of the South Peten Basin, whilst the Corozal Basin represents the eastern extension of the North Peten Basin. 

Generalized stratigraphic columns of Belize and Guatemala, marked to show those horizons where oil has been discovered and produced in both countries. (Adapted from an academic paper published in the Journal of Petroleum Geology, by Petersen, H.I. et al., 2012) First hydrocarbon exploration efforts began with Shell in 1938, who conducted geological studies through fieldwork and aerial photos, although it wasn’t until 1955 that the first well, Yalbac-1, was spudded by Gulf Oil in the Corozal Basin. Further companies tried their luck in the following decades, including majors such as Esso, Phillips, Chevron and Oxy, leading to over 75 dry wells being recorded, most of them in the Corozal Basin. However, it should be noted that non-commercial oil shows have been reported from more than 50 of these wells. 

Several factors have been put forward to explain why these drilling results may not tell the complete story. Many of the wells drilled were based on poor or non-existent seismic data and were not optimally located due to accessibility issues; some wells never reached target depths or were off-structure; and for many of the wells that revealed oil shows, production casing was not lowered to enable conventional testing to be carried out. 

Belize eventually struck oil in 2005 when a small band of geologists, led by Susan Morrice and Jean Cornec, made the groundbreaking discovery at Spanish Lookout, in the Corazol Basin, where light oil was recovered from a number of intervals in the Lower Cretaceous Hillbank Formation, a 75–100m section of dolomite punctuated with evaporate and sandstone units. This was followed by another discovery in 2007, from the overlying stacked dolomite/anhydrite sequences of the Yalbac Formation at the Never Delay area just outside of Belmopan. These fields are now under the ownership of the private company Belize Natural Energy (BNE). 

Belize’s stratigraphy is considered to be poorly or incompletely defined, partly due to a deficit of good outcrop exposures and fossil control as a result of extensive dolomitization of its carbonate sections, which is especially true of northern Belize. In general, the Corozal Basin can be described as carbonate-dominated, whilst the Belize Basin sees more clastic input in large parts of the section. 

Seismic Data Repository 

Xunantunich. (Source: Gareth Williams) According to the GPD archives, seismic reflection surveying first began in Belize during 1965-66, when Shell started to acquire low fold data in the offshore area between the coastal towns of Belize City and Dangriga, and around the Turneffe Atol. Thereafter, acquisition programs were carried out almost every year by the permit holders of blocks in both basins up until the early 1980s, with a few surveys then completed in 1991/92 that mark the end of what the GPD refer to as ‘vintage’ data. The total length of vintage 2D data acquired over this time is reckoned to be just short of 10,000 km, but the remaining records of these data are almost entirely in the form of traditional post-stack sections printed onto paper or film. 

Transforming these legacy sections into something potentially useful requires the application of seismic vectorizing, a process which involves carefully scanning the original sections and reconstructing the rasterized peak/trough wiggle traces into vector waveforms. The science and art of doing this has been perfected for over two decades by Lynx, who also bring considerable experience to bear to the practice of setting up and running national data repositories, having successfully implemented and managed the UK Onshore Geophysical Library (UKOGL) for many years. And so it was almost natural that, following an informal meeting between representatives from both parties in 2014, an agreement was inked that would enable the process of building a seismic repository for Belize to begin. A year later, 90% of the vintage data was completed to the extent that it now exists in an industry standard digital format (SEG-Y) that can be loaded into a workstation by geoscientists and interpreted. 

A website and interactive online GIS map was launched in 2016 to help draw attention to the availability of the seismic archive, and this has since been coupled with an online SEG-Y viewer so that visitors can preview example lines from all of the vintage surveys. Recently, the scope of Lynx’s remit has been extended so that modern seismic data acquired in Belize (surveys that are now publicly available following expiry of a five-year confidentiality period) will now be added to the repository, which currently includes two 3D surveys and original field (unstacked) data for most of the 2D.

  • A screenshot from the online interactive map, showing an example of one of the vintage seismic lines.

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