The long term zonal isolation is an important factor to be considered while designing cement slurries for deep High Pressure, High Temperature (HPHT) gas well. Conventional heavy weight cement systems which have been used in the past have often had to sacrifice the set cement mechanical properties such as compressive strength, permeability, and porosity, to provide a slurry design which is stable, mixable and pumpable. Changes in downhole conditions in terms of temperature and pressure can induce sufficient stresses to destroy the integrity of the cement sheath which will cause long term gas migration and sustained annular pressure. Hence, the set cement mechanical properties have to be carefully designed in order to withstand the downhole stresses especially the ones generated during the well testing and fracturing treatments. This paper will discuss the selection and the Novel Flexible and Expanding cement system and details one well case history of nine wells which is part of the upstream agreement with Saudi.
The loss of circulation during well drilling and cementing jobs is a serious problem for the oil and gas Industry. Loss of time is very costly and wellbore erosion can lead to inadequate zonal isolation putting the long-term integrity of the well in jeopardy. Lost circulation was a major challenge experienced by an operator when drilling wells in their 2011 campaign. The site geological prognosis indicated a high degree of depletion in sands and presence of natural fractures. As anticipated, severe lost circulation while drilling was experienced in these formations and drilling efficiently proved to be a challenging process due to heavy mud losses. An engineered fiber-based loss circulation control pills (EFLCC), based on special engineered fiber system and using a particle size distribution principle were developed to address this issue. The combination of fibers, special solids, and cementitious material was designed and tested in the laboratory to validate its ability to bridge the loss zone while permanently sealing the losses allowing further drilling to the next casing point. This paper presents the case history and field application of these novel engineered fiber-based loss circulation control pills for the successful treatment of heavy mud losses to formation in wells in offshore gas fields in Indonesia. The paper also includes a discussion of the methodology, material properties and applications.
Losses while drilling are a serious concern to oilfield industry. Loss of expensive drilling fluid increases the overall cost of the well. Rig time spent curing the losses can represent significant cost overruns for the well. In extreme cases well control may become an issue. The general practice to control losses starts from diagnosis of the cause. The common solutions to manage the loss circulation problem include drilling fluid treatments involving decreasing the density, controlling the viscosity and addition of lost circulation materials (LCM), controlling the drilling parameters, and placement of cement plugs. This paper will discuss the treatment of drilling fluid with Advanced Engineered Fiber (AEF), the mechanism of action of AEF and its successful application as a solution for lost circulation in Pakistan. Introduction Lost circulation is a common problem encountered during drilling. This problem can result from minor to extremely expensive and dangerous situations. The severity and persistence of a lost circulation problem are determined by the type of formation to which fluid is being lost. Generally lost circulation can occur in cavernous or vugular formations, highly permeable zones and fractured (natural or induced) formations. OMV in Pakistan had serious lost circulation problems in the Sawan field while drilling the Sui Main Limestone (SML) and Ranikot formations. Geologically Sui Main Limestone and Ranikot formations are fractured lime stones interlayered with thin beds of sand stone and clay stone respectively. Furthermore it is hard to reduce drilling fluid density below 8.9 lbm/gal due to stability problems of the Ghazij shale overlain SML Stone (fig-1) Losses in this area could range anywhere from 3,000 bbl of mud per well in the SML formation. While drilling the Sawan-3 well more than 20,000 bbl of drilling fluid were lost and the rig spent 8 days fighting the losses using all the conventional LCM available on the rig. Three cement plugs were required to control losses and completed the well after the unsuccessful LCM treatments. Table -1 shows the volume of drilling fluid lost in some off set wells in the area. Depending on the severity of the problem several techniques and products are available, the most common technique is to pump a high concentration LCM pill with fibers, flakes or granules, alone or in combination. Indeed, the pill pumped can fail and be lost to the formation if the LCM particles are smaller than 1/3 of the pore size or fracture width in the thief zone. The LCM's effectiveness is influenced by the material type, particle size distribution and optimum concentration determined by the lost circulation scenario (pore size or fracture width).To control losses into a rock matrix, the drilling fluid must contain some particles that are at least one-third as large as the flow path.
HPHT well subjects zonal isolation and long term cement integrity into critical factor to achieve long term production life. Repeated cycles of high differential pressure and temperature tend to break bonding between cement, casing and formation. Microannulus as consequence of debonding will provide space. At gas wells, it will provide space for gas migration which may lead to sustained casing pressure. Providing zonal isolation is also important to ensure there will be no communication between two different formations or reservoirs This paper discusses the design, execution and evaluation of cement technology implemented at 9 5/8-in HPHT intermediate liner. Special softwares were used to simulate gas migration risk and stress analysis to cement sheath. High risk gas migration and microannulus were expected based on sofware results. An expandable cement system was identified as a solution and deployed successfully. In order to achieve better understanding of behaviour of cement slurry at field application, laboratory experiments were performed. To achieve long term cement integrity, it is not only about design of cement slurry, mud removal is one of the key factor need to be considered. Best practices were perfomed to achieve the highest mud removal efficiency. Expansion test was perfomed by using pressure curing chamber at 247°F. Expansion was detected for six days simulation which was considered as enough based on stress analysis simulation of compression, traction and microannulus cement sheath performed. It was indicated that expandable cement managed to eliminate microannulus which was created by pressure and temperature changes. Evaluation was performed by locating pressure sensor at the A annulus of 9 5/8-in liner and 13 3/8-in casing. The sensor indicated zero pressure at the annulus while drilling next two more section and during the production life of the well
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