TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractIn fields with potential for scale buildup, downhole video offers a unique and cost effective method for obtaining direct visual data of scale in the wellbore environment. In a recent study, Chevron successfully used downhole video logging to obtain actual images of scale deposits in producing wells. These images were used to design and optimize a scale removal program in the West Coalinga field of Central California.

Most heavy oil production occurs from shallow, unconsolidated sandstone reservoirs. Unfortunately, these reservoirs are prone to multiple forms of formation damage including sand and fines migration, clay swelling, organic precipitation, scale, and formation alteration caused by thermal EOR. In many cases, standard industry practices fail to remove or prevent this formation damage from occurring for a variety of reasons including improper identification of the damage mechanism and selection of inappropriate remedial or prevention techniques. This paper will present a comprehensive approach for optimizing production in heavy oil fields prone to formation damage. It will discuss the analytical methods used to identify and quantify multiple formation damage mechanisms, propose guidelines for remedial design, introduce some methods of statistical analysis used to determine optimal remedial treatments, and suggest some methods for implementing a field program for the remediation and prevention of formation damage. Overall, this paper should provide a useful methodology for improving production in any heavy oil field prone to multiple formation damage mechanisms. Introduction Heavy oil fields are known for their susceptibility to formation damage. Unfortunately, this fact is often overlooked due to the high permeability associated with these reservoirs and thus the inherent belief that some formation damage is acceptable. The issue is further complicated by the fact that numerous formation damage mechanisms can be encountered and identifying the damage mechanism as well as actually quantifying its impact on production remains difficult. Overcoming formation damage is also hindered by the relatively low economic margins typical of many heavy oil fields, which often places an economic limit on the design and treatment of damaged wells. Combined, these factors often lead to an acceptance of sub-optimal production, or worse, the belief that formation damage is not a serious problem in heavy oil fields. Fortunately, there are numerous tools available for engineers and field operators to assist in identifying and overcoming formation damage. However, to be successful, a comprehensive approach is required. This approach requires several steps including identification, quantification, remediation, and prevention. If implemented properly, production can be quickly optimized leading to higher well productivity and lower operating costs. Damage Mechanisms in Heavy Oil Fields Heavy oil reservoirs are prone to almost every formation damage mechanism known. The shallow unconsolidated and poorly sorted nature of these reservoirs make sand control a continuous effort. Other damage mechanisms encountered include fines migration, paraffin and asphaltene deposition, various forms of scale, clay swelling, and in the case of thermal EOR, dissolution and alteration of the sandstone formation.1,2 Many of these damage mechanisms are compounded by the methods used to produce heavy oil including slotted liners, screens, and gravel packs. These can plug off from any number of the damage mechanisms and over time, further reduce inflow and well performance.

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThe design and implementation

In the past few years, downhole video has emerged as a viable and cost-effective means for analyzing various wellbore problems. Despite this, numerous misconceptions concerning the cost, application, and complexity remain. In an effort to provide insight into the proper application and selection of this unique tool, the results of over 30 downhole video logs conducted by Chevron in the West Coalinga field will be presented and discussed. Examples will include images obtained of damaged liners, casing holes, and corrosion problems, as well as their application to remedial well work. Other examples will include images of the in-situ producing environment, in particular, the ability of downhole video to image fluid entry and the impact of various wellbore plugging agents including scale and organic precipitation. Finally, the total cost of running a video log and the steps necessary to prepare a well will be compared to more traditional means of logging. Overall, this paper should provide valuable insight for anyone considering the use of downhole video. Introduction Downhole video was first used in the Coalinga field in 1998. Since then, video technology has been used extensively to record images of casing damage, liner damage, wellbore plugging, and analysis of remediation procedures. In many cases, downhole video technology has become the logging method of choice due to its unparalleled ability to accurately assess the downhole environment. This said, downhole video technology is not applicable in all cases. Downhole Video Technology The first attempts to use camera technology in a wellbore occurred in the 1940's at the request of a local pump manufacturer located in the San Joaquin Valley. The early attempts led to the capture of black and white pictures on stereoscopic slides that were used with a viewfinder to create a 3-D aspect. These early cameras were very large in diameter and limited to depths of up to 1000 feet. Technology led to further developments in downhole video deployment in the 1960's through development of coaxial cable capable of handling the transmission of high frequency signals required for motion video. In the early 1990's, an Electro-Opto logging cable was developed utilizing fiber optic technology1. This greatly enhanced the ability of the camera by addressing pressure constrains and opening up new applications in production logging. The downhole video camera uses Electro-Opto fiber optic technology. This technology produces real time video at 30 frames per second with a working temperature of 257 F to 350 F, depending on tool diameter. The tool is made up of three basic components - the electrical chassis, the centralizer, and the "Backlight" camera. The light source is positioned above the camera in the same housing. This facilitates indirect illumination, as well as creates an unobstructed view of the wellbore. This coupled with a surfactant applied to the camera lens allows the operator to descend into the well through an oil/gas column of several thousand feet and maintain the ability to image the wellbore where a clear fluid is the primary medium. This technology is routinely to pumping wells with minimal preparation. In many cases, by shutting in the well and allowing the fluids to separate, clear real time vidoe can be achieved. Today, downhole video technology is a viable diagnostic tool for many downhole applications. Downhole video technology has been used for numerous applications including mechanical inspection, open hole logging, formation damage analysis, fishing operations, as well as detection of fluid and sand entry. Downhole Video Limitations Before using downhole video to image a well, it is important to understand the limitations or disadvantages of the system. Limitations include well preparation, cost, and the inability to piggyback the system with other logging tools.

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractCyclic steam injection is commonly used to improve production in heavy oil fields. The process consists of injecting high temperature steam down the wellbore, and after a soaking period, returning the well to production. In general, high temperature steam improves productivity by decreasing oil viscosity and increasing gravity drainage. However, the same high temperature steam used to improve performance can alter the mineralogy of the gravel-pack materials and near wellbore formation. Recently, a study examining the impact of cyclic steam on the productivity of gravel-pack completions was completed in the West Coalinga field. The study found cyclic steam to be extremely detrimental to the long-term performance of gravel-packed slotted liners due to dissolution and reprecipitation of various minerals found in the gravelpack materials and localized formation. The conclusions were based on analysis of production profiles of gravel-packed wells undergoing cyclic steam injection and the actual physical inspection of gravel-packed liners cut and pulled from producing wells. Given the results of this study, caution is recommended when considering cyclic steam operations on gravel-packed liners.