Petroleum, history of exploration

Exploration for hydrocarbons (oil, gas, and condensate) is commonly acknowledged to have begun with the discovery at Oil Creek, Pennsylvania, by "Colonel" Edwin Drake in 1859. However, this was only the start of the modern global era of technology-driven advances in exploration. Traditionally, oil exploration was conducted by recognizing seeps of hydrocarbons at the surface. The Chinese, for example, used oil (mostly bitumen) obtained from seeps in medication, waterproofing, and warfare several thousand years ago. They frequently dug shallow pits or horizontal tunnels at seep locations but also, as early as 200 b.c., drilled down as much as 3,500 ft (1,067 m) using rudimentary bamboo poles (making Drake's 69.5 ft [21.2 m] over 2,000 years later seem puny by comparison). In Baku, Azerbaijan, there are still gas and oil seeps that are permanently on fire and have been used to light caravanserai since the times of Marco Polo and the Silk Route. Similarly, seeps were recognized and exploited in the Caucasus (Groznyy region of Chechnya), Ploesti in Romania, Digboi in Assam, Sanga Sanga in eastern Borneo and Talara in Peru.

Even Drake's well, the first to intentionally look for oil in the subsurface, was based on direct identification of seeped hydrocarbons at the surface. Initially, the oil produced was used to provide kerosene for lamps, but the later invention of automobiles drove up demand and ushered in modern methods of oil exploration. In fact, most oil until the turn of the twentieth century was in one form or another related to seep identification. However, one theory developed during this time was to have a profound impact on exploration. In the mid 1800s, William Logan, first Director of the Geological Survey of Canada, recognized oil seeps associated with the crests of convex-upward folded rocks and employed a geologist, Thomas Hunt, to formalize his "anticlinal theory." This idea, however, was only recognized as a viable tool for exploration when Spindletop was discovered on the Gulf Coast of Texas in 1901. For the next 30 years, the anticlinal theory dominated exploration, to the extent that many believed that there were no other types of hydrocarbon accumulation. As a result, geologists became critical to understand the structural configurations of rock sequences which, when combined with seep occurrences, proved to be the keys to discovering the main oilproducing provinces of the United States, Mexico, and Venezuela. For a period of time before World War I, Oklahoma, Texas, and California were the World's leading production areas.

Around the turn of the century and up until the 1950s, the main exploration tool used for finding oil was the use of intensive and detailed geological mapping. This was frequently in terrain that was remote and inhospitable. The early pioneers working their way through the jungles of Burmah, India (Burmah oil company, now part of British Petroleum ), and Borneo (Shell), the deserts of Iraq or the mountains of Iran (the Anglo-Persian Oil Company that became British Petroleum), would conduct detailed evaluations of the nature and distribution of rock units. These rock units represented potential reservoirs, seals, and source units, as well as frequency, orientation, and geological history of folds or faults that could act as traps for the migrating hydrocarbons.

It took until the 1920s for explorers to realize that hydrocarbons could occur in situations where no anticline was preserved. For example, it was noted as far back as 1880 that oil was trapped in the Venango Sands of Pennsylvania, not in the form of an anticlinal structure, but by the lithologies occurring in a moving palaeoshoreline. In fact, oil trapped by stratigraphy was discovered more often by chance rather than design even until the 1970s. By the 1920s, mapping of surface features was complimented by the development of seismic refraction, gravity , and magnetic geophysical methods. In particular, gravity and seismic methods proved effective in locating oil trapped against buried salt domes in the onshore Gulf of Mexico . At this time, another significant advance in exploration of the subsurface took place with the application of geophysical techniques by the Schlumberger brothers to measuring properties of rocks and fluids encountered whilst drilling for hydrocarbons. In France in 1927, they initially measured the resistivity of the rocks in shallow wells (drilled primarily for water distribution), but later went on to add other electric, sonic, and radioactive logging tools. It is now even possible to log porosity, permeability, mineralogy , and fluids and image the structures and rock types downhole. Ultimately, these developments have been one of the main reasons why Schlumberger has become one of the largest electronics companies in the world.

Aerial remote sensing for features favored for hydrocarbon accumulation became an important and effective technique, particularly in areas of sparse vegetation cover following World War II when low-cost, rapid reconnaissance of large areas became feasible. Large-scale features such as faults and folds could be identified and targeted for detailed seismic acquisition. In the 1970s, this capability was improved dramatically by the use of satellite remote sensing technologies (LANDSAT).

From the 1940s to the 1960s, there were important developments in the understanding of the controls on lateral and vertical variations within reservoir sequences. In particular, the new discipline of sedimentology used modern depositional analogues from around the world to understand the nature, distribution and controls over ancient reservoir sequences. There was also much interest generated over the discovery of carbonate oil-bearing reservoirs in West Texas and Canada (Leduc Reef), and recognition that modern inter-tidal carbonate-evaporite sequences in the UAE had equivalents in ancient reservoirs. These developments lead to the discovery of many super giant carbonate oil fields in the United States (Yates Field), Mexico (Posa Rica), Middle East (Kirkuk), and Russia (a number of Siberian oil fields).

Other tools such as geochemistry , developed during this period, have helped to quantify the level of maturity and the nature and distribution of source potential in a region. Micropalaeontology was developed in Tertiary Basins such as Trinidad and the Caucasus for horizon identification and correlation using planktonic foraminefera, but spread rapidly to the United States Gulf Coast. Now, geochemistry and biostratigraphy, including palynology (the study of spores and other organic matter), have become standard tools in the explorationist's armory.

Also beginning in the 1970s, there was a significant advance in the power and reduction in size and cost of computers that has lead directly to a dramatic increase in the ability of geophysicists to acquire, process, and interpret large quantities of seismic data. Initially, this was in the form of 2-D reflection seismic onshore, but this trend has continued to the present day and now oil companies regularly undertake, mostly offshore, 3-D seismic surveys and even 4-D field surveys. Three-dimensional surveys are repeated over the same area every few years to monitor fluid movement within reservoirs and thereby optimally manage hydrocarbon recovery. Highly complex three-dimensional models of the subsurface can be displayed on sophisticated workstations or in the form of a fully enclosed room where staff can be totally immersed in the data using special glasses and can "walk through" the reservoirs to, for example, choose the optimal location and direction of wells.

Exploration for oil and gas has progressed dramatically in the last 30 years, driven forward by the ever-increasing power and capabilities of the computer. As a result, it now takes only a fraction of the time required 20 years ago to find and develop oil fields. However, technology in itself does not find oil or gas fields; it frequently requires a flash of inspiration that is the mark of a true explorer to discover some of the major new exploration plays in such areas as Equatorial Guinea, Angola, Nigeria, Trinidad, the Gulf of Mexico, and the northern Canadian Rockies.

See also Fuels and fuel chemistry; Petroleum detection; Petroleum, economic uses of; Petroleum extraction