Although the 21st year could be gone after the Minami Nagaoka gas field started production, this period was also the years which had the problem including the matter described below and have continued planning of that measure, execution, and surveillance. The measure taken by the meantime has just been going to change along with development of the technology which surrounds oil industry. This report describes how tradition of the know-how of the well finish including the work over carried out until now, technology, and skill is performed exactly, and aims at a well service free.
Japex did the workover operations in Yufutsu gas field, Hokkaido in 2004. It was an unique and challenging workover operations. The well had been suspended because more than 3,500m of 1.25in coiled tubing was left in 3.5in production tubing. This well had to be stimulated due to the damage of reservoir, so the coiled tubing must be retrieved prior to stimulation. The situation was very serious because of the narrow annulus of the string, so selection of the pipe and tool size were restricted, accordingly the yield strength of such macaroni pipe and tools were so weak. After an examination, the plan was made to retrieve the coiled tubing from inside of 3.5in production tubing by using 1.9in work tubing, thru-tubing fishing tool and slim-hole wireline tools. This operations were performed by drilling rig in case of contingency. Wireline chemical cutter was one of the key tools in our program. Unfortunately it was not working properly so we abandoned to use it and change the plan to swallow the coiled tubing with continuous overshot and 1.9in work tubing. Continuous overshot made an excellent progress and almost all the coiled tubing was retrieved from the well. Then the well was circulated and cleaned with brine, the operation was done in the budget. Stimulation was performed in April, 2005, as a result, productivity was improved substantially and this project was completed successfully.
DTA (Drilling Training Alliance) in Houston, USA owned by Chevron and BP started to hold Deepwater Completions Workshop in July 2003. The Workshop includes lectures and discussions in all aspects regarding deepwater completion technologies and operations. In this report, some topics from the Workshop are reported and discussed.
The purpose of primary cementing is to provide zonal isolation during the life of the well so that the hydrocarbons can be produced safely and economically. Recently, the industry has taken the exploration and production of oil and gas to challenging environment such as high pressure, high temperature (HPHT), Steam Injection and Deepwater. Recent experience has shown that conventional cementing procedures could be inadequate under these conditions to provide zonal isolation. From all accounts, the experience in Japan in this regard has been very similar to the global experience.
One of the main functions of cement is to prevent fluid communication between formations or to surface throughout the life of the well, including after abandonment. Even when cementing operations has provided a good initial hydraulic seal, changes in downhole conditions can induce stresses to destroy the integrity of the cement sheath resulting in a loss of zonal isolation. We present an analysis of the mechanical response of set cement in a cased wellbore to quantify this damage and determine the key controlling parameters. The results show that the thermo-elastic properties of the casing, cement, and formation play a significant role. The type of failure, either cement debonding or cement cracking, is a function of the nature of the downhole condition variations. This analysis allows us to propose appropriate cement mechanical properties to avoid cement failure and debonding. We show that the use of high compressive strength cement is not always the best solution and, in some cases, flexible cements are preferred. A new approach to cement design was undertaken to fulfill the requirement. A cement system with improved flexibility to resist stress cracking was designed and implemented. This system is engineered to have a low Young's Modulus while maintaining relatively high compressive and tensile strengths as compared to conventional cement systems. The permeability of the set cement is very low, yielding a material that is highly resistant to attack by corrosive fluids. Finally, the system can be designed to be gas tight to prevent gas migration. This paper presents data on the new cementing design methodology and technologies used as well as simulation comparisons and large scale laboratory test results.
In order to extend the service lives of corroded 13%Cr steel tubing strings, batch treatment of corrosion inhibitor was considered. However, there was no inhibitor for chromium containing steels. As a result, the candidate inhibitors recommended by leading chemical suppliers were inhibitors suitable for carbon steel in hot, CO2 environments. The inhibitors were evaluated for their adsorption behavior and film persistency not only for bare 13%Cr steel but also for corroded one. Judging from the estimated corrosion mechanisms, water displacement ability of an inhibitor from corrosion pits and other corrosion products were considered to be very important. Therefore, the water displacement ability and the ability for making the corrosion products oil-wet were also evaluated in the laboratory. The selected inhibitor from the series of laboratory tests was served for a field test. A well was inhibited by a spire-headed tubing displacement method. The inhibitory effect on the corrosion was monitored by iron counts in produced water. After the tubing inhibition, the iron counts stayed low for fifty days, then gradually rose and returned to its original figure at three months after the tubing inhibition. This treatment life was much longer than we had expected, and that length could not be explained by the conventional adsorption theory. The inhibitor's ability of water displacement and making the corrosion products oil-wet was considered to play very important roles in this very long treatment life. In addition to the abovementioned new findings, very important mechanistic information was reconfirmed in the series of laboratory tests. The additional inhibitory effect of liquid hydrocarbon is very important, sometimes much larger than that of inhibitor itself, from the stand point of the degree of inhibition.
Real-time diagnosis of bit wear while drilling has been a fundamental interest for drilling engineers. It has been inferred from previous studies that the degree of tooth wear for a roller cone bit might be correlated with the increases of cone rotation speeds during drilling. This implies that monitoring cone rotation speeds could be an effective diagnostic method of tooth wear for roller cone bits. However, there is no practical means to directly measure cone rotation speeds in the field so far. Instead of direct measurement, the author developed an estimation method of cone rotation speeds from roller cone bit vibration data. The method is an application of signal detection from random data using cross-correlation function. An estimate of cone rotation speed can be obtained as an inverse problem solution by maximizing the cross-correlation between measured bit vibration and a vibration time history simulated using bit dynamics model for a single cone expressed as a function of cone rotation speed. Validation of the method was made by applying the estimation procedure to experimentally measured vibration data for 8-1/2" milled tooth bits. The developed method could simultaneously estimate the rotation speeds for all of the three cones with considerably high accuracy in various drilling conditions.
In the future petroleum exploration, it is presumed that technology for prediction of reservoir distribution become more important to reduce geological risks. Methods for prediction of reservoir distribution, based on the intervention of conceptual geological models, are applicable in the exploration of subtle traps such as stratigraphic traps which explorationists must face in the near future. Sedimentology and Sedimentary Geology may provide conceptual geological models which is utilized to predict reservoir distribution. The 17th International Sedimentological Congress will be held in Fukuoka, Japan on August, 2006. Having activities within ISC2006 FUKUOKA, an international academic meeting of Sedimentology, is the favorable chance for Japanese petroleum development companies not only to impress their presence and intellectual faculties but also to appeal their social contributions.
Fission-track (FT) dating is a radiogenic method of age estimation based on the accumulation of damage trails left by nuclei that are expelled during spontaneous nuclear fission of the uranium isotope 238U. Significant amounts of uranium occur in rock-forming minerals such as apatite and zircon. Data obtained by FT dating such as grain ages of internal and external surfaces, different closure temperatures of both surfaces, and distribution patterns of FT lengths give us valuable information as a geological clock and thermometer. Two examples from the Niigata district demonstrate the application of FT dating.