Rus detachment in Dammam Dome, Eastern Saudi Arabia: a new soft-sediment structure as a ‘sensitive stress sensor’ for the Zagros collision

This paper describes in detail hydroplastic structures, which are ‘odd’ kinematic indicators in the basal part of the Eocene Middle Rus Formation. Such structures were previously ignored or falsely interpreted. These hydroplastic structures are found in the massive limestone exposures on the King Fahd University of Petroleum and Minerals (KFUPM) campus. They occur in relation to a principal displacement zone along the boundary/interface between the Lower/Middle Rus, which is referred to as the Rus soft-sediment detachment. The structures are fist-sized vugs associated with carrot- or comet-trail imprints (VCT structures) which were previously translated calcite geodes that have been weathered out. VCT structures show transport/slip towards the NNW (345°) and are found on flat to low-dipping surfaces classified as Y, R and P shears with respect to the orientation of the Rus detachment. Palaeostress analysis indicates an Andersonian transtension stress regime, though it does not facilitate the activation of the Rus soft-sediment detachment. Detachment activity occurred due to the negative effective principal stress σ3′ and the abnormally low frictional coefficient caused by fluid pressure. The soft-sediment Rus detachment can be considered a ‘sensitive stress sensor’ for the Zagros collision since it indicates the Arabian platform’s instability in the wider area of the Dammam Dome during the Late Eocene. This instability is attributed to the inception of the Zagros collision, which was previously considered to occur during the Oligocene based on the well-established pre-Neogene unconformity.

Working Mechanism of Pile Group with Different Pile Spacing in Dense Sand

Complex interaction mechanism exists between the pile group and soil. To realize the pile-soil load transmission mechanism in detail, the failure pattern of pile groups installed in dense sand considering different pile spacing was investigated by means of laboratory experimental model test and three-dimensional discrete element method. The results suggested that the narrow pile spacing was beneficial to the development of the pile tip resistance, and it enhanced the bearing performance of the pile group at the initial stage of settlement. The pile spacing changed the shaft resistance pattern with modification of the strain energy mechanism released within the subsoil. The pile group with 6b pile spacing had higher composite group efficiency. A joint fan-shaped displacement zone was formed beneath the pile tip for the pile group with 3b pile spacing; this pile foundation presented the block failure mechanism. The sand displacement beneath the cap for the pile group with 6b pile spacing mainly located on the upper part of the piles, the sand displacement around both sides of the piles presented asymmetric, and a relatively independent fan-shaped displacement zone was formed beneath the pile tip.

Laminar Displacement of Non-Newtonian Fluids in Parallel Plate and Narrow Gap Annular Geometries

Based on certain maximum gradient approximations similar to those used in lubrication theory, the miscible displacement of one non-Newtonian fluid by another is analyzed. The fluids are assumed to be of the power-law type and the displacement occurs in a parallel-plate system under conditions where dispesion effects associated with molecular diffusion and convection are negligible. The results provide predictions of displacement efficiency in provide predictions of displacement efficiency in terms of certain characteristic groups, including the density ratio of the phases, an effective viscosity ratio, a flow rate group, and the power-law slope parameters. The results should represent first-order parameters. The results should represent first-order approximations to slow flow displacements occurring in many well completion operations. Introduction The displacement of one fluid with another has been a subject of keen interest to the oil industry for many years. Although numerous studies have been undertaken on the mechanics of miscible and immiscible displacement and the associated flow instabilities and dispersion phenomena, there is still a wide range of practical problems that cannot be treated within these previous theoretical and experimental studies. This is particularly true with regard to problems involving rheologically complex, or non-Newtonian fluids. Such fluids are encountered in many facets of petroleum production, and the displacement of (or by) these fluids is crucial to current drilling and well completion practices. Such displacement problems are continually encountered in cementing operations, where one Non-Newtonian fluid is displaced with another. Although various laminar and turbulent flow techniques have evolved over the years, the basic fundamentals underlying these displacement practices go well beyond the current status of displacement theory and experimentation. Under normal circumstances these accepted practices generally lead to satisfactory cementing operations, even though it is doubtful that optimal or near-optimal displacements are ever achieved. However, in more abnormal and demanding operations these practices are often inadequate. In order to achieve optimum results, the basic flow phenomena involved in non-Newtonian displacement must be carefully understood and methods must be developed to predict displacement characteristics in terms of the rheological, kinematic, and geometric conditions involved. Unfortunately, the technology related to non-Newtonian displacement is quite limited. Most of the work to date has been concerned with the specific aspects of displacing a given drilling fluid with another (or with a given cement mixture) for a limited range of flow conditions. Only recently have the effects of rheology, density differences, flow rates, and eccentricity been considered in any quantitative detail. Specifically, Graham has presented a calculation technique for predicting the total volume of cement required to predicting the total volume of cement required to displace completely a drilling mud from an eccentric annulus under conditions of plug-flow displacement. Eccentricity is accounted for by dividing the annulus into segments and treating each segment individually. Unfortunately, displacements under plug-flow conditions are seldom realized in practice and, hence, such calculations represent only crude approximations. In a more recent study, Clark and Carters have presented experimental data on mud displacement efficiency under conditions simulating wellbore environment at 8,000 ft. These investigators indicate that higher displacement efficiencies are obtained under turbulent flow conditions. However, these results were obtained using many displacement-zone volumes of the displacing phase. In practice, because of economic considerations, only a few displacement-zone volumes of the displacing phase can be used. It is still not clear whether turbulent displacement is to be preferred in these latter situations. SPEJ P. 169