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Since mid-1981, 36 wells have been cemented in the Williston Basin with a cementing system diametrically opposed to conventional cementing designs used for bonding across massive salt members. Since implementation, along with the use of relaxed invert emulsion oil mud, not one casing problem has arisen in the wells where these systems were used.
The Rocky Mountain region provides a myriad of cementing problems. One of these is cementing massive salt members. This is of particular interest to Gulf in their particular interest to Gulf in their operations in the Williston Basin of North Dakota and Montana where numerous and sometimes severe casing problems have been encountered by Gulf and other operators. The salt intervals of interest in the Williston Basin are the Jurassic Dunham salt, the Triassic Pine salt, the Permian Opeche Evaporite, the Pine salt, the Permian Opeche Evaporite, the interbedded salts of the Mississippian Charles Formation, and the Middle Devonian Prairie Evaporite. Also of interest to the Drilling and Production Engineer is the Cretaceous Dakota Formation which is known for its corrosive waters. Doglegged and/or collapsed casing severe corrosion can arise in wells where any or all of these formations are not isolated from the casing by cement. The solution is to insure a contiguous, uniform cement sheath from the top of the Cretaceous Dakota to below the Ordivician Red River. This solution entailed three areas of engineering endeavor: (1) casing design, (2) drilling fluids, and (3) cement. Only the last of these will be detailed in this paper.
DISCUSSION WILLISTON BASIN:
The cementing procedures outlined in this paper are followed by Gulf Oil in all paper are followed by Gulf Oil in all Williston Basin drilling. The Little Knife Field of North Dakota is used specifically because this field is where the cementing procedures outlined below were perfected.
The little Knife Field is located within the counties of Dunn, McKenzie and Billings in North Dakota. To date, 164 wells have been drilled by Gulf. All but two wells in the field produce from the Mississippian Mission Canyon Formation at +9,750 feet (2,972 meters). Two wells are producing from the Devonian Duperow Formation. Of the 164 wells drilled since November, 1976, 13 wells are temporarily abandoned due to low production, 17 wells are plugged and abandoned due to casing failures, plugged and abandoned due to casing failures, 44 wells have casing problems (doglegs, corrosion or tight spots) but are still producible, and 33 wells are still flowing and have not been entered since completion. This means that 37% of the wells drilled in the field have some casing damage. This number may be as high as 57% when all the flowing wells are equipped to pump. Of the remaining 57 pumping wells with no problems, 17 (30%) have been pumping wells with no problems, 17 (30%) have been drilled with a relaxed invert emulsion mud and cemented with a low salt cement.
Three problem areas evolved during the planning, drilling and completion of wells in planning, drilling and completion of wells in the Williston Basin in general and the Little Knife Field in particular. The first problem recognized and addressed was insufficient casing collapse design through salt sections. All casing strings run in the Little Knife Field have been designed with 1 psi/foot (22.6 KPa/m) collapse minimums through all salts encountered and in fact a 1.5 psi/ft collapse (33.9 KPa/m) factor is common across the upper salt members in the Little Knife Field.
A number of cementitious materials used for cementing wells do not fall into any specific API or ASTM classification.These materials include: Pozzolanic materials include any natural or industrial siliceous or silico-aluminous material, which will combine with lime in the presence of water at ordinary temperatures to produce strength-developing insoluble compounds similar to those formed from hydration of Portland cement. Typically, pozzolanic material is categorized as natural or artificial, and can be either processed or unprocessed. The most common sources of natural pozzolanic materials are volcanic materials and diatomaceous earth (DE). Artificial pozzolanic materials are produced by partially calcining natural materials such as clays, shales, and certain siliceous rocks, or are more usually obtained as an industrial byproduct. Pozzolanic oilwell cements are typically used to produce lightweight slurries.
Setting openhole cement plugs has historically been a difficult task. Often, several attempts are required to set a cement plug before one is obtained that has sufficient strength for sidetrack and is at the intended depth. It is our opinion that unstable flow behavior, resulting from the heavy weight of an unset cement plug resting on top of a lightweight mud, is one of the main causes of plug failure. The common practice of using open-ended drillpipe or tubing to spot the plug is also a major contributor to unsuccessful plug setting. This paper presents a placement technique and materials design that have resulted in a successful plug on the first attempt in many field cases where previous plug setting was difficult. Several case histories are presented. To examine the instability problem associated with cement plugs, an experimental investigation was conducted. This investigation consisted of setting cement plugs of known densities and rheological properties on top of drilling muds having known properties. The experiments were conducted using lucite pipe to simulate hole or casing and using copper tubing as the drillpipe. In each test, the hole was initially filled with drilling mud. Then, cement was displaced through the simulated drillpipe to displace drilling mud up the annulus. The ability of the cement plug to remain where it was placed was observed visually and correlated with other experimental observations. This paper includes the results of the experimental paper includes the results of the experimental investigation. The main conclusion of this investigation is that the stability and quality of a cement plug for sidetracking or any other purpose can be greatly improved through the use of our new placement technique.
Early in 1980, a research project was directed toward determining the possible causes of repeated failures in setting cement plugs, particularly sidetrack plugs, as reported for some operating areas. Those reported failures seemed more common when plugs were placed in wells with drilling muds weighing less than 10 lbm/gal [1198 kg/m ]. As part of the investigation, a detailed literature study was initiated. More than 150 articles dealing with many aspects of setting cement plugs were screened. For detailed study, a smaller group of papers that appeared to have the most relevant information was selected. Those articles and a few others are given in the General References at the end of this paper. The chosen group of articles gave a consensus concerning techniques and slurry design considerations needed for successfully setting cement plugs (a list of those considerations that we concur with is given in Appendix A). After investigating several of the reported failures, it was concluded, with some exceptions, that those industry-recognized techniques given in Appendix A were being followed. However, plug failures were still occurring. In a previous paper, Beirute investigated the behavior of a liquid cement plug once it is left alone in the well. By means of laboratory experiments and a mathematical model, he showed that heavy cement slurries placed on top of lightweight muds form unstable interfaces which because of the adverse gravitational forces may cause the fluids to flow, contaminating the plug or causing it to move downward and, therefore, contributing to the plug job failure. His observations when running his experiments correlate quite well with field descriptions of reported cement plug failures. Since those observations are considered quite significant, they are given in Appendix B. A series of experiments were designed to investigate the phenomenon of cement plug stability in the wellbore. The idea was to determine whether this was a major contributor to cement plug failures, particularly when setting plugs by the balanced plug method, without using a bridge plug or any other form of support "table" below the plug. Also, if plug instability was found to be a serious cause, of failure, it was the intention of the investigation to discover ways to control the problem.
The experiments were conducted in a simulated wellbore constructed out of clear lucite tubes approximately 18 in. [46 cm] long and 1.75 in. [4.4 cm] ID as shown in Fig. 1. Some tests were run in longer tubes (approximately 3 ft [0.9 m] long). To simulate the drillpipe, 0.5-in. [1.3-cm] copper tubing was used. The drilling mud and cement slurries that were used in the experiments were mixed as closely as possible to those used in the field. A low-solids, nondispersed (LSND) drilling mud that weighed 9.0 Ibm/gal [1078 kg/m ] was used in the experiments. This type of mud is used extensively and was chosen since it represented the greatest density difference between the cement slurry and the drilling mud that would be encountered in the majority of situations where cement plugs would be set. A list of the fluids used in the experiments is given in Table 1. The initial experiments were conducted to simulate placement techniques as closely as possible. placement techniques as closely as possible. JPT
Khanna, Manu (Cairn - Oil and Gas Vertical of Vedanta Ltd) | Sarma, Phanijyoti (Cairn - Oil and Gas Vertical of Vedanta Ltd) | Chandak, Krishna (Cairn - Oil and Gas Vertical of Vedanta Ltd) | Agarwal, Apurv (Cairn - Oil and Gas Vertical of Vedanta Ltd) | Kumar, Animesh (Halliburton) | Gillies, James (Halliburton)
Abstract Well RXY is located in the Ravva offshore field in the Krishna-Godavari basin (India) and was intended to produce significant crude from a secondary reservoir section. This paper presents a case study concerning rigless remediation of microchannels in the cement packer (placed in the annulus of the production tubing and casing to isolate the producing zone) and discusses laboratory development of a customized epoxy resin system, simulations to estimate channel size, three-dimensional (3D) displacement modeling, drillout after placement, and evaluation post-placement. An epoxy resin system was selected to seal micro-annuli in a cement packer and restore zonal isolation because of its ability to develop high compressive strength, potential to resist significant strain, and its solids-free formulation. This resin system was pumped followed by an ultrafine cement slurry comprising a fine-particle high-surface-area cement blend that can penetrate small channels more easily compared to conventional cement. The top of fluids was simulated for various cases as per channel size estimations, and 3D displacement modeling was performed to incorporate fluid contamination. The strategic placement of epoxy resin and ultrafine cement focused on isolating annuli above the zone of interest. Conventional cement testing equipment was used to customize resin formulations to downhole conditions. After placement and solidification of the designed treatment, cement remaining in the tubing was successfully milled. A positive hermetical test was conducted after 48 hours of setting time, and the result was confirmed as successful. Barrier evaluation was performed using a combination of a cement bond log (CBL) tool and ultrasonic scanner. Furthermore, the acoustic impedance was post-processed to generate a derivative acoustic impedance (DZ) data set before performing the data analysis workflow. On the basis of analysis of this evaluation, the well was perforated in the pay zone interval and produced approximately 2,000 BOPD. The well was observed for several days to confirm tubing and casing isolation. The epoxy resin plus ultrafine cement blend was designed to deliver a dependable barrier. This engineering solution proved to be a highly efficient and cost-effective method for treating narrow cement channels in a deviated tubing-production casing annulus using only pressure-balanced cement placement. The epoxy resin technology has unique properties that make it best suited for remediation, particularly in tight geometries, such as in the current scenario of micro-annuli channels in a cement sheath. The resin system is solids-free (Newtonian fluid) and can provide a high-pressure seal. The system also withstands contamination (overcomes inefficient well fluid displacement), which is beneficial when prejob cleanup resources are limited. In addition, this drillable system develops compressive strength ranging from 5,000 to 15,000 psi.
Pernites, Roderick (BJ Services) | Brady, Jason (BJ Services) | Padilla, Felipe (BJ Services) | Clark, Jordan (BJ Services) | Ramos, Gladyss (BJ Services) | Callahan, Jaron (BJ Services) | Garzon, Ricardo (BJ Services) | Sama, Raymond (BJ Services) | Embrey, Mark (BJ Services) | Fu, Diankui (BJ Services) | Johnson, David (Independent Resources Management) | Richey, Nicolas (Independent Resources Management)
Abstract Increasing horizontals, narrowing annular gaps, more stringent cement regulations, fracturing with more stages and high pumping rates on top of more cost-efficient well completion are raising demand for lightweight cements, which are designed to prevent damage and lost circulation problems in weaker formations. However, many alternative lightweight materials that are more cost effective than glass beads, which are known to provide superior strength, are increasing waiting-on-cement time, thus delaying further drilling. They also struggle to deliver the required compressive strengths. This paper presents (1) recent case histories of successful field applications of new stronger non-beaded lightweight cement, (2) extensive laboratory data of various field designs with new lightweight cement versus premium commercial lightweight cements, and (3) detailed scientific study explaining how the innovative lightweight cement has provided superior fluid stability and set cement mechanical properties. The successful field trials occurred in the Permian basin for all four wells on the same pad. About 400 bbl of the new lightweight cement at 10.5 lbm/gal density was delivered to complete each cementing job with 134°F BHST and 6,000-ft measured depth. The four wells were completed with the new lightweight cement, remarkably having no glass beads despite the extremely low density. Unlike the previous job designed with commercial lightweight cement, the new cement has provided far greater compressive strength and has shown faster (18 to 24 hr) strength development. During placement, the new lightweight cement slurry has demonstrated exceptional stability with fewer additives than the previous design, thus simplifying field operations. Multiple laboratory test data at different cement densities (10.5 to 14.5 lbm/gal) for other regions confirmed the enhanced performance of the new lightweight cement in both slurry form and set cement over conventional lightweight technologies. Detailed scientific study via X- ray Diffraction (XRD) explained how the new lightweight cement provided superior set cement performance. The novelty of this work and invaluable contribution to the industry is the first successful field application of a newly developed micromaterial that provided a lighter, stronger, low-permeability, non-beaded cement that enhances wellbore integrity and provides better zonal isolation. New findings from XRD and Scanning Electron Microscopy (SEM) imaging techniques about the new micromaterial lightweight additive may provide insights for improving the performance of traditional materials.