Vortex evolution in a rotating tank with an off-axis drain

Fluid entering the periphery of a steadily rotating cylindrical tank exits through an off-axis drain hole, located in the tank's base at the half-radius. Experiments show that, though a concentrated vortex forms over the drain, it soon advects around the tank in what is at first a circular path. Though inviscid vortex dynamics predicts continued motion, our experiments show that the vortex moves inwards from the predicted circular path, finally coming to rest at approximately $50^{\circ }$ from the drain. In this final state, the vorticity is concentrated in a thin shear layer bounding an irrotational core, which passes over the drain. The broadening of the vortex structure and eventual steady-state formation are believed to be due to the growing boundary layer on the outer wall.

A Simple Strategy For Subsurface Delivery of Effective Development Wells – Field Examples

Well delivery is an expensive scope in the exploration and field development process. Among other drivers, an ideal well must be delivered safely while achieving top-quartile performance on cost, schedule and business objectives. However, delivering an ideal well amid subsurface uncertainties and tightening budgets is usually challenging. As part of the drive for continued value creation, this paper presents an empirical process-improvement initiative for de-risking and optimizing the landing of the drain-hole sections of highly deviated wells amid subsurface uncertainties and at minimal costs. A review of the conventional procedure for executing subsurface scope of the delivery of development wells has been accomplished. The review takes advantage of a combination of recent experiences in delivering four horizontal development wells in an offshore field in the Niger Delta, in addition to a catalogue of available knowledge and best practices from other fields and operators. This review culminates in an improved well delivery optimization process and practice. In addition to promoting operational HSE excellence, it increases the chance of delivering an ideal well, including the mitigation of a subsurface-related non-productive time (NPT) and other related costs. As a complement to the practice, a simple workflow is provided to aid robust decision-making and facilitate applications in practice. For completeness, relevant examples are included to demonstrate the applicability of this new process.

Delayed Action Micro-Emulsion Breaker and Its Applications to Improved Completions Operations – An NNPC/FEPDC JV Approach During Completions Operations

In horizontal open hole wells, the formation of filter cake while drilling the open hole section of the well is desirable. This filter cake serves the purpose of forming a semi-impervious layer around the reservoir drain-hole. This layer helps reduce losses considering the overbalance required for well control during drilling. It also serves as an additional structural support to keep the open hole stable when the drilling bottom hole assembly (BHA) is pulled out of hole and the screens and lower completions accessories are being run in hole. However, when thewell is put into production, the filter cake becomes a contributor to skin and poor reservoir productivity. It is therefore required to get rid of the filter cake after running the screens and the lower completion. Having procured and prepared the sand screens for deployment after drilling the open hole section, it is important that they are run to the bottom successfully with minimal damage and plugging. Usually, the open hole section of the horizontal well is drilled with specially formulated drill-in-fluids (DIF). Since this section is drilled in over balanced mode, the exerted pressure keeps the hole open so that the sand screen can be run successfully. The DIF replaces the drilling mud used to drill the earlier hole section(s) but in addition to providing well control via overbalance and transporting cuttings from the hole to surface, it also minimizes invasion damage to the reservoir pay zone. A commonly used weighing material when densities up to 11.5ppg are required for well control is calcium carbonate (CaCO3). When densities above 11.5ppg are required (for deeper, abnormally pressured reservoirs), it becomes necessary to weight up the mud with a heavier material, usually barite + CaCO3. During the drilling process, this overbalance pressure exerted on the reservoir forces the CaCO3 out of the DIF solution and it forms a semi-impervious filter cake on the sand face of the reservoir. This desirable filter cake helps minimize excessive fluid losses into the reservoir hence limiting invasion and damage. It also contributes to the structural integrity of the open hole, keeping it stable prior to running of the screens. Depending on the weighting material used in the drilling of the reservoir drain-hole, the micro-emulsion breaker (MEB) can be designed to break down the filter cake and any undisolvedparticulates can be mobilized and water-wetted and can be then flowed during production or injection. The challenge is that depending on the lower completion configuration, it may take some time to get the wash pipe and work string out of the lower completion and close the formation isolation device. In some cases, it is possible for the formation isolation device to fail. If the Micro-emulsion Blend (MEB) is quick acting, any of these scenarios can lead to uncontrollable losses and serious difficulties in continuing the completion operation. This elucidates the need for a delayed acting MEB treatment. Lab tests and analysis involving the exact DIF /filter cake and various compositions of the MEB at downhole conditions to arrive at the required delay in action. It is critical to ensure that the delayed action does not result in reduced efficacy of the treatment. Hence, the MEB is not diluted for slow action but rather it is engineered combinatorially with a retarder and downhole mild acid generating microemulsion chemistry that gradually generates the necessary mild acid that will slowly dissolve the bridging materials (eg. calcium carbonate) in the mud withtime and allows the full strength of the MEB to take effect after the stipulated delay period. This paper will focus on the lab analysis and iterations to arrive at an optimal MEB blend.

Pengaruh Jarak Antar Drain Hole Terhadap Penurunan Muka Air Tanah pada Lereng Tambang Terbuka Batubara

The presence of groundwater on the slopes of the mine, which means that the slopes are saturated with water, will cause a decrease in slope stability. Drain hole is a method that can be applied to decrease groundwater level on a mine slope. This research was conducted to determine the effect of horizontal distance between drain holes on the mine slope on the decrease in groundwater level (groundwater drawdown). Groundwater flow simulation on the slopes of an open pit coal mine with 3 scenarios, without drain holes, 100 m horizontal space between drain holes, and 50 m horizontal space between drain holes, was carried out to answer the goal of this research. The results obtained from the simulation, the third scenario with a distance between drain holes of 50 m has the maximum result compared to the other two scenarios, which are the percentage of groundwater drawdown of 54.1% and groundwater discharge of 167.3 L/s. So it can be concluded that the denser the horizontal distance between the drain holes on the mine slope, the higher the groundwater drawdown on the slope.