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Seteyeobot, Ifeanyi (Department of Petroleum Engineering, Covenant University) | Uma, Joshua A. (Department of Petroleum Engineering, Covenant University) | Enaworu, Efeoghene (Department of Petroleum Engineering, Covenant University)
Drilling in HT/HP wells has adverse effects on drilling fluids. At high temperatures and pressures, the chemical additives used in drilling fluid formulations experience thermal degradation above 107°C (225°F) leading to strong variations (reduction) in rheological and filtration characteristics. Locally derived Rice-Husk and grounded Plantain peels were used to improve the rheology and filtration properties of back-loaded oil based mud at HT/HP behavior, and the results were compared to industrial additives like Sodium Carbooxymethylcellulosics (CMC), Polyanionic Cellulosics (PAC), and Sodium Polyacrylates (SPA). This research was centered on the use of three oil-based mud samples from a particular field in the Niger Delta basin. The samples included; a reconditioned mud, a freshly prepared mud (both with standard industry additives), and a back-loaded mud respectively. Seven  different mud property tests were carried out on the samples to determine their current state. After that, the back-loaded mud was upgraded with the locally derived additives and it's rheological and filtration properties were observed and compared to the results of the first two samples. The effects of high temperature and high pressure on the stability of the locally-derived additives were also observed. This was paramount because the chemical additives underwent thermal degradation at these conditions. The most significant finding is that the locally derived additives worked at the same level or probably better than the industrial additives.
The novelty of this research was to evaluate the potential of locally derived additives for improvement of mud rheology and filtration in comparison with industrial additives. Also, a reduction in the cost of purchasing foreign viscosifiers and filtration control additives by patronizing locally derived additives hence reducing the overall cost of a mud program. Lastly to make sure that wastes like rice husks and plantain peelings are recycled by usage in drilling mud formulations so as to prevent environmental problems such as heaping of refuse on the streets.
Oil and gas exploration and production in Nigeria is geared towards meeting the energy need of its populace and also generate revenue. However, oil field chemicals used in oil and gas activities are sources of environmental pollution, causing various degrees of harm especially to the aquatic components of the environment. Most ascertained detrimental effects of oil field chemicals on organisms are generally laboratory based investigations. These have not considered synergistic and antagonists effects of these chemicals under various environmental conditions on organisms and the ecosystem. A research that incorporates both field and laboratory studies to investigate the effects of oil field chemicals in the natural environment would be of great use to provide a wholistic data for scientists. Such research would consider both synergistic and/or antagonistic effects of these chemicals under the natural environment with its varing conditions. The result obtained from such study would significantly enhance - integrated catchment management (ICM), further limnological studies/assessment, information for policy redress on contamination and pollution abatement, and remedial activities to ensure a sustainable healthy environment.
Ahmari, Abdulrahman (Saudi Aramco) | Al Ghamdi, Saleh (Saudi Aramco) | Hanbzazah, Shadi (Saudi Aramco) | Yateem, Karam (Saudi Aramco) | Ahmed, Danish (Saudi Aramco) | Bal, Moustapha Bal (Schlumberger) | Elsherif, Tamer (Schlumberger) | Molero, Nestor (Schlumberger)
Early applications of technology systems relevant in the past in simple wells have become inadequate or suboptimal for conducting field-wide operations for more complex wells, especially in a regime of rising development costs. For field developments requiring extended reach wells, such as Saudi Aramco’s Manifa project, distinctive new technologies need to materialize, improve, and be rapidly diffused to execute comprehensive plans and make significantly higher returns from capital technology spending in the field. Coiled tubing (CT) reach, multilateral access, effective stimulation treatments, and production or injection profiling remain challenges for engineers in ultra-deep wells. Discrete technology solutions adequate in the past are no longer sufficient for creating value.
The scope of this paper is to present the evolution of technology systems over a timeline in rigless stimulation and logging intervention activities for achieving field development outcomes. Field examples are provided to illustrate how these technologies have evolved to ensure strategy-to-technology alignment of numerous separate well intervention solutions for successfully developing a giant carbonate oil field in readiness for a major production milestone.
As a result of continuous inclusion of technology-based exercises at a project level, rigless activities have been completed over 60% faster than when well intervention campaigns started nearly five years ago. Technology is continuously advancing and leading to newer, unprecedented, and cost-efficient ways to deliver value. The gains from technology evolution include challenging engineers to conceive of future possibilities, such as the introduction of more robust tools that exceed the performance of past or current systems. The evolution of the change cycle challenges engineers to adapt, consolidate gains, and continue the evolution process.
The Manifa field in Saudi Arabia was discovered in 1957 and its dimensions were around 18 km in width and 45 km in length. Sustained production started in 1964 with all the initial wells in Manifa as offshore wells. By 1977, some 17 wells had been drilled mostly offshore. Because of low demand the field was mothballed in 1984. In 2006, a grassroots field redevelopment plan commenced while drilling and active development began with major capital spending on both relative shallow offshore waters and onshore areas. Figure No.1a is a snapshot of some technological achievements in the Manifa field. To adequately cover operations in the field, 27 manmade islands were developed and connected by a causeway (Arukhe, et al, 2013).
Cementing is one of important and crucial issues in oil field especially for high pressure and gas bearing formations. It is difficult to achieve a good zonal isolation in such formation types where pressure is abnormal and formation fluid contains corrosive fluids and gases. A common problem associated with highly over pressurized zones is cross flow after cementing. Fluid flow from an over pressured zone to a low pressure, high permeability zone can lead to deteriorating the existing production hardware. Work over operations that attempt to repair cement voids including perforation, squeezing and use of casing patches or scab liners are not recommended as they do not provide long lasting results. In one of onshore fields in Saudi Arabia there is a persistent problem related to cementing at high pressure zones. Recently, communication between A (abnormally over pressurized zone) and B (low pressure zone) formations is occurring due to long term sea water injection with increasing frequency, and has resulted in production interruption in several wells. This paper addresses the problems through investigating field practices including drilling, cementing, and completion. It also reviews the field reports and cased hole logs. A three-month study was conducted to evaluate the effects of formation-A water on cement, where the cement was exposed to formation-A water under down hole conditions. The tests for permeability, mechanical properties TGA and EDXRF are presented, in addition to discussions of some of the preliminary findings.
Ugonoh, Mohammed (Sahara Energy Field Ltd.) | Anifowose, Hussein (Sahara Energy Field Ltd.) | Ajayi, Olajumoke (Sahara Energy Field Ltd.) | Sijpesteijn, Casper Kaars (Sahara Energy Field Ltd.) | Adedotun, Wali (Sahara Energy Field Ltd.) | Obeta, Chukwudi (Sahara Energy Field Ltd.)
The use of offset mud weight in combination with geologic information and drilling operations report can be very useful in estimating formation pressure in appraisal and exploratory well planning. It has been established that conventional shale pressure modeling is an effective tool for pore pressure prediction William Standifird et al 2005. The model can be updated as new data is acquired to reduce the uncertainty window and optimize drilling. This paper aims to generate shale based pore pressure profiles for the Sahara wells in northern depositional mega structure of the Niger delta using equivalent depth method and compare shale based gradient with predicted gradient from offset mud weight
The offset mud weight was expressed in pressure gradients allowing for computation of hydrostatic head of the mud and subsequently backing out the overbalance. This provided a fair estimate of the formation pressure. The estimated pressure was corrected for hydrocarbon buoyancy. The fracture gradient was derived from the leak off test of the offset well data. The lithostatic gradient is based on the regional gradient for the northern depo belt of Niger delta of Nigeria. In the shale based pore pressure estimate, the overburden gradient was modeled by superimposing the density log of the wells due to the paucity of density log. The Leak off Test of two offset wells was also utilised used to define the fracture gradient. Equivalent depth method was used in the computation of the pore pressure in the three wells
Comparison of the formation pressure profile generated using the offset mud weight from X, Y and Z wells and shale based pore pressure prediction using proprietary software indicated the two methods shows tolerable difference fit for purpose well planning.
Dossary, Abdulla (Saudi Aramco) | Al-Majed, Abdulaziz A. (King Fahd University of Petroleum and Minerals) | Hossain, Enamul (King Fahd University of Petroleum and Minerals) | Rahman, Muhammad Kalimur (King Fahd University of Petroleum and Minerals) | Jennings, Scott S. (Saudi Aramco) | Bargawi, Riyadh Ahmad (Saudi Aramco)
Cementing is one of the most important and crucial issues in the oil field, especially for high pressure and gas bearing formations. It is difficult to achieve a good zonal isolation in such formation types, where pressure is abnormal and formation fluid contains corrosive fluids and gases. A common problem associated with highly over-pressurized zones is cross-flow after cementing. Fluid flow from an over-pressured zone to a low-pressure, high-permeability zone can lead to deterioration of the existing production hardware. Work over operations that attempt to repair cement voids — including: perforation, squeezing and use of casing patches or scab liners — are not recommended, as they do not provide long-lasting results. In one onshore field in Saudi Arabia, there was a problem related to cementing at high pressure zones. Recently, communication between A (abnormally over-pressurized zone) and B (low-pressure zone) formations occurred due to long term sea water injection, and has resulted in production interruption in a few wells. This paper addresses the problem through investigating field practices, including: drilling, cementing, and completion. This study also reviews the field reports and cased hole logs. A three-month study was conducted to evaluate the effects of formation-A water on cement, where the cement was exposed to formation-A water under downhole conditions. The tests for permeability, mechanical properties TGA and EDXRF are presented, in addition to discussions of some of the preliminary findings.
Effective placement of stimulation fluids on horizontal, long interval and/or gravel-packed wells is critical for cost-efficient production enhancement. Successful case history work in 19991, using precision rotary jetting technology (R-Jet) on the end of coiled tubing (CT), demonstrated to the oil and gas industry that fluid placement is a key factor in removing near-wellbore damage and optimizing well stimulation treatments.
This paper will review continued efforts relating to precision rotary jet technology including extensive laboratory tests using a full-scale gravel pack (GP) model. Tests were videotaped for further visual study. Established guidelines applying lab results, computer modeling, and field validation provide a well-engineered, non-damaging (low nozzle pressure) treatment for optimum stimulation performance. Proper damage identification coupled with skillful stimulation fluid design are important steps to a successful job and will be highlighted in the global R-Jet case histories.
The data clearly shows that a highly effective method of placing stimulation fluids into a completion, such as sand control screens or slotted liners, is to use CT-conveyed, rotary speed-controlled, forward-angled radial jets. This technique yields 360° coverage of the treatment area, is more efficient than traditional bullheading and CT methods and allows reduced treatment volumes to be considered. It applies to a wide selection of completions including horizontal wells which can now be successfully stimulated at reasonable costs.
The formation of petroleum residue and deposits is a recurrent problem in low API gravity or heavy oil reservoirs and reservoirs with significant pressure and temperature fluctuations. It is also a challenge in fields where recent well interventions has pushed pipe dope into the perforations resulting in severe loss of native formation permeability and productivity.
This paper discusses the application of a unique solvent acid dispersion that offers one step stimulation of reservoirs damaged with both plugging solids and organic deposits. Conventional acid systems including the numerous patented HF - HCl and organic acid blends dissolve the plugging solids and cementitious materials but cannot stimulate sandstone reservoirs damaged with organic deposits or a combination of plugging solids , fines migration and organic deposits. In fact, the formation of acid induced sludge is common.
However, this acid - solvent blend dissolves asphaltene and paraffin deposits, prevents the formation of wax crystals and removes organic residue and inorganic materials simultaneously. A special surfactant train acts synergistically with the acid blend, prevents acid induced sludge and leaves the rock surfaces strongly water wet. Overall treatment efficiency was increased especially in gravel packed intervals by using a rotating jetting tool although success has also been recorded using the bullheading option. Recent experience has shown the acid blend is particularly suitable as a spearhead for injection wells. Optimum solvent loading for effective stimulation is between (10 - 20) percent depending on reservoir temperature, suspected damage mechanism and the severity of relative permeability effects.
Unique experience detailing standard lab / field practice and exceptional results for several wells in the Niger Delta is the focus of this paper. Wells treated with this unique blend either as spearhead for other specialty acid systems or as a one step treatment show dramatic and sustained productivity increases of between (50 - 150) % relative to initial well data. The system has been proven to be successful in most types of completion architecture. Key technical and economic performance indicators including skin factors, production rates, specific productivity indices, payback time and treatment cost indicate this low viscosity acid blend is both technically proficient and cost effective.
Introduction and Justification
The in-situ remediation of damage caused by organic material deposited in the near wellbore region from well construction and intervention operations i.e. from POBM's, pipe dope, e.t.c. And from the producing system itself (waxes, resins, and asphaltenes) has historically been tackled using either one or a combination of the following measures: Hot oil - water treatments, Hot water - solvent combination, Solvent - surfactant - dispersant trains and crystal modifiers.1
The use of hot oil / water treatments is useful in the treatment of surface equipment clogged up with wax. Though these measures have attained a given degree of success even in reservoir stimulation applications, their continued usage has been proven to concentrate higher melting point carbon molecules in existing deposits, hereby making the resulting deposits more resistant to further heat treatments. This method has also been shown to cause significant formation damage by the way of negative relative permeability effects.
Solvents and solvent / surfactant /dispersant trains are excellent means of organic damage removal in the reservoir. However, the extent of their organic carrying abilities is limited by temperatures below the cloud point of the organic material / solvent combination. Large quantities of solvents are typically required i.e., 100 lbs. of xylene will just dissolve 6 lbs. of C36 paraffin at 100°F.2 However, the use of the proper combination of chemicals (determined by proper lab tests) can reduce treatment volumes and costs considerably. The use of crystal modifiers or pour point depressants provide a more effective means of preventing deposits in the reservoir but are usually cost prohibitive.
Acid stimulation of oil and gas reservoirs, with a view to increasing well productivity, has been applied since the late- 19th century. Initially applied in carbonate reservoirs, the technique was extended to more complex mineralogies, over a number of years. However, it's fair to say that acid stimulation of wells is the exception rather than the rule. This probably stems from the complex, heterogeneous nature of formation minerals and the unpredictability of their response to conventional oilfield acid formulations. With inappropriate acid designs, or poor job procedures, even the best candidate wells can be damaged, sometimes irreversibly.
This paper discusses the current state-of-the art in matrix acidising and makes the case for the wider implementation of acidising, as a cost-effective method for production enhancement. It reviews the many rules used today in the design of acid treatments and how these rules have evolved with improvements in our understanding of the interactions between acids, formation constituents and well tubulars. The paper also reviews the rationale behind the use of additives such as corrosion inhibitors, iron control agents, clay control additives, surfactants, solvents, anti-sludges and diverting agents, etc. and makes general recommendations on appropriate loadings, where applicable.
Finally, the latest developments in acidising are considered, including the use of novel acid systems, to overcome many of the problems inherent in earlier formulations. Innovative equipment design, coupled with real-time monitoring capabilities, improved placement techniques and environmentally-friendly materials, are helping to transform acidising into a valuable asset in the quest for optimum performance from every oil and gas well. The paper references many key publications and provides the engineer with an upto- date overview of the state-of-the-art in this very important discipline.