On the basis of structural style and differences in Late Cretaceous evolution, the carbonate platform in northern Oman and the allochthonous wedge comprising deepwater sediments and oceanic crust in the Oman Mountains form distinct structural domains. Imbrication associated with the emplacement of the Semail Ophiolite and predominantly SW-verging thrusting of the Arabian Platform margin culminated in the late early Campanian. The structural grain of NW-trending thrust faults and contractional folds contrasts markedly with the style and grain of the region immediately south of the Oman Mountains (our study area) and implies strong strain partitioning. Kinematic indicators from subsurface data, combined with the age of growth faulting, provide the basis for the interpretation that maximum horizontal stress was oriented NW-SE in this foreland region rather than NE-SW during the Campanian. The dominant tectonic control on the formation of faults is believed to have been an oblique “collision” of the Indian Continent with the Arabian Plate during the Santonian-Campanian. Deformation in this domain was dominated by distributed strike-slip and normal faulting. This period of faulting was significant for two reasons: (1) The faults both enhanced existing structures and formed new traps. They also allowed vertical migration of hydrocarbons from Palaeozoic reservoirs (e.g. Haushi clastic accumulations) into Shu’aiba and Natih carbonates above. Until that time, some 75 Ma ago, oil was retained in Late Palaeozoic and older traps. This period of deformation is a “Critical Event” within the context of Oman’s hydrocarbon distribution.(2) Faults with NNW and WNW orientations that developed at that time appear to be directly associated with important fracture systems that affect the productivity of several giant fields comprising Natih and Shu’aiba carbonate reservoirs (e.g. Lekhwair, Saih Rawl). Following this tectonic event, late Maastrichtian to Palaeocene uplift and erosion in excess of 1,000 m, is recorded by truncation of the Aruma Group and Natih Formation, as well as part of the Shu’aiba Formation below the base Cenozoic unconformity. Seismic velocity and porosity anomalies from Lekhwair field in the northwest to the Huqf-Haushi High in the southeast, provide additional support for the areal distribution of this event. Around the Lekhwair and Dhulaima fields, the circular to elliptical subcrop pattern below this unconformity does not support the notion of a peripheral bulge related to the emplacement of the allochthon. The stress field changed during the late Cenozoic with the opening of the Red Sea and Gulf of Aden, and the collision of the Arabian Plate with the Iranian Plate. NE-SW-oriented maximum horizontal stress during the late Cenozoic led to the formation of major folds resulting in, for example, the surface anticlines over the Natih and Fahud fields as well as causing inversion along the Maradi Fault Zone. This may also have led to the uplift of the Oman Mountains. The regional northerly subsidence caused by crustal loading of the Arabian Plate gently tilted traps during the Pliocene-Pleistocene from Lekhwair to Fahud.

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Electric submersible pumps (ESPs) are used in oil production as effective means of artificial lift. All the major componets of an ESP are put in a long and slender housing. Seal section, located between the motor and the pump, consists of a number of chambers. All the chambers, the base and the head of the seal are connected to the ESP housing through threaded joints between the seal guide and the housing. Lock plates are welded to the housing over each threaded connection to provide additional constraint. The paper presents experimental results to examine different configuration options for lock plates on a type of high power ESP seal housing failed during operation. The paper summarizes the results of mechanical and metallurgical tests, mechanical strength and vibration analyses along with appropriate recommendations. This paper brings into focus the importance and necessity of analyzing even relatively simple and minor components like seal lock plates for safe operation of ESPs. Background In the oil industry, electric submersible pumps (ESPs) are used for the recovery of oil as an effective means of artificial lift. The ESP submersible pumping systems consist of both surface and downhole components. The main downhole components are electric motor, seal, gas separator, pump and electric cable. Seal section is located between the motor and the pump. The seal section has five important functions: to provide mechanical connection between the motor and the pump, to provide a thrust bearing to carry the load of the pump shaft, to prevent well fluids from entering the motor, to provide a reservoir for the motor oil and to.equalize the pressure between the motor and the well bore. The seal section, in general, consists of a number of chambers. All the chambers are connected to the housing through threaded joints between the seal guide and the housing. Similarly the base and the head of the seal are connected to the housing through threaded joints. Lock plates are welded to the housing over each threaded connection to provide additional constraint to the separation of the joints. The design of ESP components is very special because of its long and slender shape and the stringent operational requirements within the oil well borehole. The requirement of high power ESPs for high capacity wells is pushing the design process even further requiring careful consideration of all major components. During operation of the ESP, the housing is subjected to torque generated in the motor-pump shaft. The transient torque during start-up, which is expected to be several times higher than the steady-state value, has detrimental effects on the ESP components including seal housing lock plates. In addition, the torsional vibration of the motor-pump shaft also gives rise to fluctuating torque on the system. This increases the possibility of loosening the threaded joints in the seal housing leading to catastrophic failure of the ESP. Recently, in one of the ESP installations, a lock plate of one seal failed leading to the interruption in production. It was felt important to carry out the failure analysis of the lock plate and to examine different options for putting the lock plates on the seal housing to avoid recurrence of such failure. Objectives The objectives and scope of the present work are as follows:To identify the failure mode of the failed lock plate.To estimate and compare the torque carrying capacities of the joints for three suggested arrangements of lock plates on dummy seal housings.To give recommendations for avoiding such failure. Samples of Lock plate One lock plate which failed and a new piece (before welding to the seal housing) were available for testing and investigation, see Fig. 1.

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractElectric submersible pumps (ESPs) are used in oil production as effective means of artificial lift. All the major componets of an ESP are put in a long and slender housing. Seal section, located between the motor and the pump, consists of a number of chambers. All the chambers, the base and the head of the seal are connected to the ESP housing through threaded joints between the seal guide and the housing. Lock plates are welded to the housing over each threaded connection to provide additional constraint. The paper presents experimental results to examine different configuration options for lock plates on a type of high power ESP seal housing failed during operation. The paper summarizes the results of mechanical and metallurgical tests, mechanical strength and vibration analyses along with appropriate recommendations. This paper brings into focus the importance and necessity of analyzing even relatively simple and minor components like seal lock plates for safe operation of ESPs.