Mud Return Research Articles

Mechanical analysis of mud return on deepwater drilling riser system

The process of mud return generates complex forces on the deepwater drilling riser system. However, the specific mechanism and effect of these mud forces on the deepwater drilling riser system remain unclear. To address this gap, an analysis methodology is proposed to investigate the mechanism and effects of mud forces. Mechanical and numerical models of the deepwater drilling riser system, taking into account mud return, are established based on the analysis methodology. The mechanical model incorporates centrifugal force, Coriolis force, inertial force, and friction force. Both the individual and comprehensive effects of these mud forces are thoroughly examined. The results show that centrifugal force and Coriolis force contribute to an increase in the lateral displacement of the riser. Friction force can decrease the lateral displacement of the riser. Inertial force can change the amplitude of riser vibration. Among these forces, friction force emerges as the most significant factor. The analysis results indicate that the maximum effect of friction force is 5.15%.

Cuttings transport in maxi HDD boreholes with front reaming and one way drilling mud return technologies

Cuttings transport becomes critical important when horizontal directional drilling (HDD) technology has been used more often in long distance and large diameter oil and gas pipeline construction in rocks. Front reaming (FR) and one way drilling mud return (OWDMR) were not new in oil and gas well drilling, but they were rarely used in HDD industry compared to the traditional back reaming (BR) and two way drilling mud return (TWDMR). FR and OWDMR technologies, when they were used in HDD, were designed mainly for highly non-leveled HDD projects to overcome some difficulties such as the recycling of drilling mud. Along with these technologies is that the cuttings need to travel longer distance to the ground surface. In addition, the effect of the drill rod rotation on the cuttings transport does not exist because hole bottom mud motor is usually used in FR. To find a solution for this problem, the cuttings transport mechanism was analyzed based on the drilling mud hydraulics, and then, an equation of cuttings transport distance was derived. It found that the average drilling mud velocity in the annulus and the consistency index of drilling mud are the two most important factors related to the cuttings transport distance. To help with the cuttings transport, a new MMH drilling mud system, which provides a high consistency index and a low flow index, was used in rock HDD projects, instead of the common Bentonite-water drilling mud system.

The return of drilling fluid in large diameter horizontal directional drilling boreholes

The return of drilling fluid (drilling mud) in large diameter horizontal directional drilling (HDD) boreholes is a very important issue related to mud pressure, cuttings transport and pull back force, but this problem has not been fully solved in previous research due to the complexity and uncertainty of downhole conditions. The calculation methods of mud pressure loss in the borehole annulus are briefly introduced and the equation using a Power Law model is adopted to study the drilling mud return. A typical reaming hierarchy of a large diameter HDD project has been used to study the return direction of drilling mud and volumes of drilling mud return to the exit and entry points. The research results disclosed that the drilling mud can return to both exit and entry points at the same time, with a large majority of the drilling fluid returning to the exit point if the reamer is closer to the exit point, and vice versa. A parametric study has been conducted to find out the effect of changing parameters in the calculation equation on the drilling fluid return. The drilling mud return for those boreholes with the exit point and entry point located at different elevations has also been discussed. Finally, different types of reamers and other factors such as borehole collapse and borehole shape were taken into the consideration of drilling mud return.

Ultra-deepwater blowout well control analysis under worst case blowout scenario

Because of the high frictional pressure losses in kill lines in ultra-deep water wells, it is challenging to control the blowout under worst case blowout scenarios. The operational parameters need to be carefully controlled to avoid exceeding the operational limitations such as breaking the formation or exceeding available pump pressure limit. In this study, dynamic kill simulations of multiphase flow are carried out to evaluate the operational parameters during the kill process. The simulations account for transient changes including frictional pressure losses, u-tube effect and fluid density variations. By optimizing the operational sequence with regards to, kill mud density, pump flow rate, pump down staging, relief well drillstring and trajectory, blowout can be controlled without exceeding the operational window. This paper shows that 10,390 bbls of the kill mud, 8000 psi pump pressure limit, optimum flow rate arrangement, and minimum 270 min required to get full kill mud return to the sea floor during the well kill operation. Through the aid of advanced transient software models, assessment of the required capacity to kill a blowout enables development of realistic contingency plans to ensure that well control can be re-established in case of an ultra-deep water worst blowout scenario.

Particle Size Distribution of Top-Hole Drill Cuttings from Norwegian Sea Area Offshore Wells

Measurement of top-hole drill cuttings particle size distribution in offshore drilling from floating rigs is not straightforward because these sections are drilled without a marine riser. In two drilling operations, a riserless mud return system was used, which made it possible to measure the particle size distribution. Still, because of the reactivity between loose shale and water, such measurements are not simple. A measurement method was developed in the field during the drilling of these two wells. The development of this method is described to assist and simplify similar measurements in the future. Likewise, the results are presented to allow scientist to use proper particle size distributions in offshore cuttings spreading analyses.

Advanced Drilling Simulation Environment for Testing New Drilling Automation Techniques and Practices

Summary Newly developed drilling automation systems locate a computer interface between commands issued by the driller and instructions transmitted to the drilling machinery. Such functions are capable of faster and more precise control than can be achieved by an unaided operator and thus can help drilling within narrow margins. To ensure that these systems work properly in all circumstances, an advanced drilling simulator has been developed to enable testing under a wide range of simulated conditions. The environment described in this paper uses hardware in the loop (HIL) simulation to verify that the automation techniques being tested respond correctly in real time. Rigorously validated physical models of the drilling process simulate the response of the well to the commands given to the drilling machines. Abnormal drilling conditions (e.g., packoffs, kicks) and equipment or machine-related problems (e.g., plugged nozzles, power shortage) are convincingly recreated. The drilling simulator models the behavior of surface equipment such as the activation of gate valves to line up different pits or the flow in the mud return. It simulates changes in the drilling fluid properties when mixing additives to the mud. It is therefore possible to focus training sessions on cooperation between different groups at the wellsite. This is particularly useful when planning the introduction of drilling automation that involves new work procedures as a result of automation and adaptation of the drilling team to a new operational environment. Drilling operations are becoming more and more complex. Automation has the potential to provide large improvements in efficiency and safety, but automation technologies must be implemented correctly at the workplace. Just as the aviation industry has used simulated environments for decades, drilling simulation environments are the key to the safe and successful implementation of drilling automation and the development of crew skills to face future challenges.

豪州沖イクシスガス田海洋掘削におけるライザーレスマッドリターンシステムの使用実績

INPEX Browse Ltd. has drilled 6 wells in the Browse Basin in order to appraise the production permit WA-285P from 2000 through 2004 (at the 1st and 2nd Drilling Campaign). All of wells have encountered stuck pipe problems while drilling the unconsolidated Grebe formation sandstone and they have provided a lot of Non Productive Time (NPT) due to fishing or sidetrack. According to the desk top study of Grebe, which was performed after drilling in 2004, it was concluded that the stuck pipe problems result from the collapse of unconsolidated sand, in other words, such collapse is caused by the absence of an effective filter cake capable of stabilizing the well bore. Eventually, INPEX Browse Ltd. has decided to drill the unconsolidated Grebe formation sandstone by closed circulation system using drilling mud instead of Seawater.In order to achieve this objective, Riserless Mud Return (RMR) system was introduced by AGR (Norwegian Company) before 3rd Drilling Campaign. Through this system, all three (3) wells have been successfully drilled without any hole collapse and no NPT was recorded. That is a major improvement rather than last two (2) drilling campaign and RMR system was demonstrated as one of an effective procedure to drill unconsolidated formation in Browse Basin.

Analysis of Riserless Drilling and Well-Control Hydraulics

Summary Riserless drilling is an unconventional technique using a relatively small diameter pipe as a mud return line from the sea floor instead of a large diameter marine riser. The schemes were developed in the late 1960s to reduce wear on blowout presenters and to make drill pipe re-entry easier by balancing internal and external subsea well pressures. However, these concepts were not implemented at that time because water depths were shallow, and technology was not available. In the Gulf of Mexico, exploration attempts have been made in areas which have more than 7,000 ft water depth. A conventional large diameter riser requires a vessel with huge weight and space capacities, large mud volumes to circulate through a riser, and numerous casing points because of the relatively low separation between the formation pore pressure and fracture pressure, especially in the Gulf of Mexico. These problems may be reduced significantly by applying riserless drilling. Therefore, riserless drilling is one of the attractive alternatives for economically exploring oil fields in deep water. The concept of riserless drilling currently has many unsolved problems such as system configuration and well control. This paper presents basic concepts of riserless drilling and a brief review of problems associated with conventional marine riser drilling for deep water applications. The paper also presents hydraulics and well control considerations for riserless drilling with comparison to conventional riser drilling.

Improved Cementing Practices Reduce Cementing Failures

Abstract The key to successful primary cementation is a hydraulic seal in the annulus area to inhibit flow of formation fluids. To accomplish this, all or a large percentage of drilling fluid must be displaced with good quality cement. Placement of cement in the annulus is probably the most critical phase of the cementing process, Many papers have been published on this topic(1–4). Most authors agree that a number of factors influence the displacement process. Several test programs have been conducted using scale models to investigate several displacement parameter (3–5). As a result of laboratory investigations and field observations a number of practices have been recommended. While these practices are valid and have a sound basis, it is not possible to apply all or the parameters in many field situations. Ideally, 100% displacement efficiency is the objective, but even in controlled laboratory conditions this is very difficult, if not almost impossible to attain. Displacement efficiency is defined as the cemented area divided by the total annular area (Fig. 1). To evaluate displacement practices and their significance in special field conditions, a field test program was conducted, the results of which were used to develop casing cementing procedures to optimize displacement efficiency. CORS Computer Program The first step involved conducting an extensive field study to determine what the common practices were and what was done in the field. A persistent problem encountered while conducting the field study was lack of complete operation data(1). To overcome this, a computer data base system was developed to efficiently store and extract cementing operations information. Field data, laboratory tests and remedial cementing operations were combined into one complete well history. Figure 2 represents an outline of the Cementing Operations Retrieval System (CORS) computer program. CORS has proven to be most valuable when determining field practices, and relating them to cementing successes and failures. Field Testing - Fluid Calipers A program was conducted to investigate displacement procedures in the field utilizing fluid calipers (Fig. 3). This procedure has been used by other researchers in similar investigation(6,7). A fluid caliper determines the amount of mobile drilling fluid in the wellbore. A marker is placed in the drilling mud which can be detected at the mud return line. Various types of markers have been utilized, and it was found that the most effective is the carbide pill, if a mud logger is on location. Acetylene is detected by the gas chromatograph at the flow line. If a mud logger is not available, a visible dye pill is used, consisting of an oil base paint mixed with polymer and sometimes, coarse material such as sawdust to make the marker more visible at the shale shaker. The following describes the fluid caliper procedure.Run a multi-arm caliper log over the open hole interval to determine total hole volume with casing in the hole.Determine mud pump efficiency by isolating the suction tank and correlating pump strokes with the volume pumped from the tank.

Cementing Displacement Practices Field Applications

Study of the factors contributing to high mud-displacement efficiencies while cementing. An extensive cementing-operations data-base was developed to relate historical problems to current operational practices. These historical data were combined with field testing programs to determine the significance of various displacement parameters. As a result, a practical cement placement program was developed. Since implementation of this progam, the numbers of primary cementing failures and remedial cementations have decreased

Postanalysis of Abnormal Cementing Jobs With a Cementing Simulator

Summary Postanalysis often cannot be applied because of lack of prediction and real-time performance data. Proper postevaluation includes collection of actual job performance data and comparison with predicted cementing performance. A comprehensive cementing simulator is required that accounts for fluid properties, well geometry, changing displacement and mud return rates, and the free-fall effect. Such a simulator has been used successfully in the design of many cementing operations and quite frequently in actual jobs to monitor the progress of the operation. In this paper, case histories are presented to show how this model and on-site measurements can be used for postevaluation of cementing jobs that did not perform as predicted. Two examples illustrate job problems caused by a restriction either in the annulus or in the casing; a third case points out problems associated with use of improperly calibrated pressure gauges during a cementing job.

Improved Cementing Success Through Real-Time Job Monitoring

An added advantage of recording actual performance data during the job is in postanalysis. If field surface pressure, rates, etc., have not agreed with predicted values, the cementing job should be analyzed. Analysis of abnormal jobs helps to improve well-cementing success. Cement channeling, annulus restriction, casing restriction, incompatibility of fluids, casing hardware problems, and deficiencies in job execution that are identified through analysis usually can be prevented or corrected on future jobs. Adequate real-time data are required for proper analysis of abnormal jobs.