Explorer Historical Highlights

In 1965, G.T. Philippi, a Shell geochemist, made the novel proposal that petroleum was generated from organic matter in sediments that had been buried deeply enough to be exposed to warmer earth temperatures, converting the organic matter, with heat and time, to petroleum.

American Association of Petroleum Geologists (AAPG)
Explorer Article

The AAPG Annual Convention and Exhibition will feature a variety of field trips that will bookend the meeting, spanning from March 26 to April 8.

American Association of Petroleum Geologists (AAPG)
Explorer Article

AAPG’s newest Hedberg Conference, “Fundamental Controls on Shale Oil Resources and Production,” will be held April 28-30 in Beijing, China.

American Association of Petroleum Geologists (AAPG)
Explorer Emphasis Article

Among the array of not-to-be-missed technical sessions at the upcoming 2017 AAPG Annual Convention and Exhibition (ACE), “Major Deepwater Fields of the Offshore U.S. Gulf of Mexico” is grabbing its share of attention.

American Association of Petroleum Geologists (AAPG)
Explorer Emphasis Article

Sidney Powers Memorial Award: Celebrating the career of Larry Meckel.

American Association of Petroleum Geologists (AAPG)
Search and Discovery Article

Subsurface electromagnetic (EM) measurements, namely galvanic resistivity, EM induction, EM propagation, and dielectric dispersion, exhibit frequency dependence due to the interfacial polarization (IP) of clay minerals, clay-sized particles, and conductive minerals. Existing oil-in-place estimation methods based on subsurface EM measurements do not account for dielectric permittivity, dielectric dispersion, and dielectric permittivity anisotropy arising from the IP effects. The conventional interpretation methods generate inaccurate oil-in-place estimates in clay- and pyrite-bearing shales because they separately interpret the multi-frequency effective conductivity and permittivity using empirical models.  We introduce a new inversion-based method for accurate oil-in-place estimation in clay- and pyrite-bearing shales. The inversion algorithm is coupled with an electrochemical model that accounts for the frequency dispersion in effective conductivity and permittivity due to the above-mentioned IP effects. The proposed method jointly processes the multi-frequency effective conductivity and permittivity values computed from the subsurface EM measurements. The proposed method assumes negligible invasion, negligible borehole rugosity, and lateral and vert ical homogeneity effects.  The successful application of the new interpretation method is documented with synthetic cases and field data. Water saturation estimates in shale formations obtained with the new interpretation method are compared to those obtained with conventional methods and laboratory measurements. Conventional interpretation of multi-frequency effective conductivity and permittivity well logs in a clay- and pyrite-rich shale formation generated water saturation estimates that varied up to 0. 5 saturation units, as a function of the operating frequency of the EM measurement, at each depth along the formation interval. A joint interpretation of multifrequency conductivity and permittivity is necessary to compute the oil-in-place estimates in such formations. Estimated values of water saturation, average grain size, and surface conductance of clays in that formation are in the range of 0.4 to 0.7, 0.5 micro meter to 5 micrometer, and 5×10 - 7 S to 9×10 - 7 S, respectively. The proposed method is a novel technique to integrate effective conductivity and permittivity at various frequencies. In doing so, the method generates frequency-independent oil-in-place estimates, prevents under-estimation of hydrocarbon saturation, and identifies by-passed zones in shales.

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American Association of Petroleum Geologists (AAPG)
Search and Discovery Article

The driving forces for conventional accumulations (structural or stratigraphic traps) are Forces of Buoyancy which are due to differences in densities of hydrocarbons and water. In contrast, the driving forces for unconventional tight accumulations are Forces of Expulsion which are produced by high pressures. That is an enormous difference and creates unconventional petroleum systems that are characterized by very different and distinctive characteristics. The Force of Expulsion pressures are created by the significant increase in volume when any of the three main kerogen types are converted to hydrocarbons. At those conversion times in the burial history, the rocks are already sufficiently tight so the large volumes of generated hydrocarbons cannot efficiently escape through the existing tight pore system, thus creating a permeability bottleneck that produces an overpressured compartment over a large area corresponding to the proper thermal oil and gas maturities for that basin. The forces initially created in these source rocks can only go limited distances into adjacent tight reservoirs (clastics or carbonates) above or below the source. The exact distance will vary depending on the pressure increase, matrix permeability, and fractures of that specific tight reservoir system. In general, the distances are small, in the orders of 10s to 100s of feet for oil and larger for more mobile gas systems. Those exact distance numbers are subject to ongoing investigations.   A plot of the pressure data versus elevation for a given formation is critical in determining whether an accumulation is conventional or unconventional. Conventional accumulations will have hydrocarbon columns of 10s to 100s of feet with the pressure in the hydrocarbons and that in the water equal at the bottom of the accumulation (at the HC-water contact). In contrast, the unconventional accumulations will show HC column heights of 1000s of feet with the pressure in the hydrocarbon phase and the water phase being the same at the top of the accumulation (at the updip transition zone). Those significant differences are critical for understanding and differentiating these two play types. Because the system is a pore throat bottleneck with very little or minimum lateral migration, the type of hydrocarbon s are closely tied to the thermal maturity required to generate those hydrocarbons. Thus the play concept begins with two important geochemical considerations: (1) where are the source rocks and what are the kerogen types and organic richness (TOC), and (2 ) where are they mature in the basin for oil, condensate, and gas in the basin. These parameters will very quickly define the fairway for the play. Then one has to add the critical information on the reservoirs themselves: composition (brittleness), thickness, and reservoir quality (matrix porosity and permeability). In summary, these tight unconventional petroleum systems (1) are dynamic , and (2) create a regionally inverted petroleum system with water over oil over condensate over gas for source rocks wit h Type I or II kerogen types.

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American Association of Petroleum Geologists (AAPG)
Africa Blog

Network, interact and share expertise with fellow petroleum scientists while learning the latest unconventional reservoir techniques and technologies.

American Association of Petroleum Geologists (AAPG)
Middle East Blog

Seven exciting GTWs in the Middle East Region in 2017!

American Association of Petroleum Geologists (AAPG)
Middle East Blog

You are invited to prepare a poster display for presentation for the workshops coming up this spring.

American Association of Petroleum Geologists (AAPG)
VG Abstract

Production from unconventional petroleum reservoirs includes petroleum from shale, coal, tight-sand and oil-sand. These reservoirs contain enormous quantities of oil and natural gas but pose a technology challenge to both geoscientists and engineers to produce economically on a commercial scale. These reservoirs store large volumes and are widely distributed at different stratigraphic levels and basin types, offering long-term potential for energy supply. Most of these reservoirs are low permeability and porosity that need enhancement with hydraulic fracture stimulation to maximize fluid drainage. Production from these reservoirs is increasing with continued advancement in geological characterization techniques and technology for well drilling, logging, and completion with drainage enhancement. Currently, Australia, Argentina, Canada, Egypt, USA, and Venezuela are producing natural gas from low permeability reservoirs: tight-sand, shale, and coal (CBM). Canada, Russia, USA, and Venezuela are producing heavy oil from oilsand. USA is leading the development of techniques for exploring, and technology for exploiting unconventional gas resources, which can help to develop potential gas-bearing shales of Thailand. The main focus is on source-reservoir-seal shale petroleum plays. In these tight rocks petroleum resides in the micro-pores as well as adsorbed on and in the organics. Shale has very low matrix permeability (nano-darcies) and has highly layered formations with differences in vertical and horizontal properties, vertically non-homogeneous and horizontally anisotropic with complicate natural fractures. Understanding the rocks is critical in selecting fluid drainage enhancement mechanisms; rock properties such as where shale is clay or silica rich, clay types and maturation , kerogen type and maturation, permeability, porosity, and saturation. Most of these plays require horizontal development with large numbers of wells that require an understanding of formation structure, setting and reservoir character and its lateral extension. The quality of shale-gas resources depend on thickness of net pay (>100 m), adequate porosity (>2%), high reservoir pressure (ideally overpressure), high thermal maturity (>1.5% Ro), high organic richness (>2% TOC), low in clay (<50%), high in brittle minerals (quartz, carbonates, feldspars), and favourable in-situ stress. During the past decade, unconventional shale and tight-sand gas plays have become an important supply of natural gas in the US, and now in shale oil as well. As a consequence, interest to assess and explore these plays is rapidly spreading worldwide. The high production potential of shale petroleum resources has contributed to a comparably favourable outlook for increased future petroleum supplies globally. Application of 2D and 3D seismic for defining reservoirs and micro seismic for monitoring fracturing, measuring rock properties downhole (borehole imaging) and in laboratory (mineralogy, porosity, permeability), horizontal drilling (downhole GPS), and hydraulic fracture stimulation (cross-linked gel, slick-water, nitrogen or nitrogen foam) is key in improving production from these huge resources with low productivity factors.

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American Association of Petroleum Geologists (AAPG)

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