ExxonMobil

About: ExxonMobil is a company organization based out in Irving, Texas, United States. It is known for research contribution in the topics: Catalysis & Polymer. The organization has 16969 authors who have published 23758 publications receiving 535713 citations. The organization is also known as: Exxon Mobil Corporation & Exxon Mobil Corp..

Conjectures on the statistics of ring polymers

Abstract: We present some conjectures concerning the equilibrium statistics and dynamics of ring polymers. We argue that unconcatenated ring polymers in the melt may have statistics intermediate between those of collapsed and Gaussian chains. An extremely crude (Flory-like) treatment suggests that the radius R of such a ring scales with its polymerization index N as R ∼ N 2/5. In contrast, a ring in a melt of long linear chains (of the same chemical species) should be swollen. Moreover, rings of one chemical species (A) can be compatible with linear chains of another (B), even when linear chains of A and B are not compatible. Rings in a network of fixed obstacles are also discussed. A simple analysis of their dynamics shows that the diffusion constant D of such a ring (in three dimensions) scales with its polymerization index N as D ∼ N-2. This prediction is confirmed by computer simulations. Finally, we consider a knotted ring formed irreversibly in a theta solvent, and argue that, under appropriate formation conditions, such a ring may remain Gaussian when placed in a good solvent.

Sandstone reservoir quality prediction: The state of the art

Abstract: Joanna Ajdukiewicz joined Exxon Production Research Company in 1980. She was Reservoir Quality Assessment and Prediction team lead there from 1991 to 1995 and at Imperial Oil Research Centre in Calgary from 1995 to 1997. Subsequently, she has worked a variety of Exploration Company assignments in the North Sea, Gulf of Mexico, and Middle East. Her current interests are in predicting the distribution of early diagenetic controls on deep reservoir quality. Rob Lander develops diagenetic models for Geocosm LLC. He obtained his Ph.D. in geology from the University of Illinois in 1991, was a research geologist at Exxon Production Research from 1991 to 1993, and worked for Rogaland Research and Geologica AS from 1993 to 2000. He is also a research fellow at the Bureau of Economic Geology. To guess is cheap; to guess wrongly is expensive (Chinese proverb). Reservoir-quality predictive models will be a useful element of risk analysis until remote-sensing tools are invented that accurately measure effective porosity and permeability ahead of the bit. This issue of the AAPG Bulletin highlights recent advances in a new generation of reservoir quality models that have successfully predicted porosity and permeability in diverse siliclastic reservoirs under many different burial conditions. Most previous attempts at predrill reservoir quality prediction have relied on empirical correlations or on first-principle geochemical simulations that incorporate laboratory-derived input parameters (Wood and Byrnes, 1994). The new reservoir quality models differ from previous approaches in that, although incorporating theory-inspired algorithms, they include terms with values that are explicitly designed to be calibrated by, and tested against, data sets of high-quality petrographic analyses that are linked to thermal and effective-stress histories. Petrographic observations therefore provide essential constraints in these models on the types, timing, and rates of key geologic processes affecting sandstone pore systems. This approach avoids the pitfalls inherent …

Sequence stratigraphy hierarchy and the accommodation succession method

Abstract: We propose a framework for the hierarchy of sedimentary units observed in stratigraphic data that is based entirely on the geometric relationship of the strata. This framework of geometries is assumed to result from repeated successions of accommodation creation and sediment fill (here named accommodation succession). We have modified existing hierarchal frameworks to describe depositional units resulting from accommodation successions of varying magnitude and duration, across a depositional profile. Each full succession consists of component partial succession sets that are, sequentially, lowstand—progradation to aggradational; transgressive—retrogradation; and highstand—aggradation to progradation to degradation. The terms “highstand” and “lowstand” as originally defined to label systems tracts relative to a shelf edge, and with an implied relationship between sea level and systems tracts, have been the root of confusion. We propose that these terms be used in the strict sense of the original definition, because their meaning has been lost when applied to the many depositional settings and high-resolution data sets to which the concepts of sequence stratigraphy are now applied. We propose that the concept of accommodation succession stacking be used in the interpretation of stratigraphic data within a hierarchal framework of depositional sequences, sequence sets, and composite sequences. This will allow an interpreter to accurately categorize observations, provide a basis for predictions away from control points, and develop a framework that allows revisions as higher-resolution data become available.

Geometry of frictionless and frictional sphere packings.

Abstract: We study static packings of frictionless and frictional spheres in three dimensions, obtained via molecular dynamics simulations, in which we vary particle hardness, friction coefficient, and coefficient of restitution. Although frictionless packings of hard spheres are always isostatic (with six contacts) regardless of construction history and restitution coefficient, frictional packings achieve a multitude of hyperstatic packings that depend on system parameters and construction history. Instead of immediately dropping to four, the coordination number reduces smoothly from $z=6$ as the friction coefficient $\ensuremath{\mu}$ between two particles is increased.

A compact fourth‐order finite difference scheme for the steady incompressible Navier‐Stokes equations

Abstract: SUMMARY We note in this study that the Navier-Stokes equations, when expressed in streamfunction-vorticity fonn, can be approximated to fourth--order accuracy with stencils extending only over a 3 x 3 square of points. The key advantage of the new compact fourth-order scheme is that it allows direct iteration for low~to-mediwn Reynolds numbers. Numerical solutions are obtained for the model problem of the driven cavity and compared with solutions available in the literature. For Re $1500 point-SOR iteration is used and the convergence is fast.