Low Formation Pressure Research Articles

Phase behavior characteristics and water-flooding development technical policy of weakly volatile oil in carbonate reservoirs

Abstract A fracture-pore carbonate reservoir in eastern Pre-Caspian basin was taken as an example to analyze the oil phase behavior change and seepage physical characteristics change of weakly volatile oil reservoirs with the decrease of formation pressure. Based on the analysis, the water-flooding development technique policy of the reservoir under different formation pressure was presented. Experiments show that the weakly volatile crude oil degasifies as the formation pressure decreases, with methane and intermediate hydrocarbons separated out successively, and the crude oil gradually transforms into ordinary black oil. With the separation of light hydrocarbons, the saturation of in-place oil drops rapidly, the viscosity increases, and the oil permeability reduces, leading to lower well productivity. Retention of formation pressure is a vital factor controlling the reservoir development effect. The lower the formation pressure, the lower the ultimate recovery. Given low formation pressure, water-flooding is required to recover the formation pressure. In water-flooding, the lower level the formation pressure is retained at, the lower the reasonable pressure to be recovered is, and the lower the ultimate recovery is. Compared with zones without fractures, the zone with fractures provides lower injection-production ratio when water-flooding is conducted under the same formation pressure, and its water-flooding time has more impact on oilfield recovery. Therefore, it is recommended to develop weakly volatile oil reservoir by early water-flooding in a moderate way.

Aerated Underbalance Drilling Screening Assessment at “X” Geothermal Field

<p>Fault network is a challenging problem for geothermal drilling operations. Formation fluid contains high temperature production fluid which can reach >225oC on high enthalpy system. The other consequences is that almost all fault network has low pressure or subnormal pressure. This low pressure results to a loss circulation problem. This low pressure can even go lower if the geothermal field has been exploited for a long period. A miss reservoir management, that do not re-inject sufficient amount of fluid, will cause the reservoir pressure go lower. Another problem in Indonesia is the conservation area which almost all high enthalpy geothermal system exist. The pay zone that is beneath the conservation area must be reached by directional drilling as a solution. High temperature fluid, low formation pressure and conservation areas are problems for geothermal drilling. To overcome these problems, underbalance drilling method has an advantage dealing with low pressure reservoir.</p><p><br />This paper introduces a way to screen the underbalance drilling method on a certain field. This study will help the quantitative and qualitative decision whether the underbalance drilling is feasible or not. The first phase qualitative decision is based on wellbore stability, loss circulation, reservoir damage, stuck pipe incident, hard drilling and cost benefit. Then it will go to the drilling fluid decision. And at the end as a quantitative decision for constructing a feasible bottom hole pressure window area with some hole cleaning assessment. Underbalance drilling assessment will be studied on field “X” at one of Indonesia’s geothermal field. The screening of “X” geothermal field comes with conclusions that it has an opportunity underbalance drilling can be implemented with vertical aerated drilling wells on spesific gas and liquid flow rates.</p><p> </p><p><strong>Keywords</strong>: <em>Geothermal, underbalance drilling, aerated drilling </em></p>

Transient dynamics study on casing deformation resulted from lost circulation in low-pressure formation in the Yuanba Gasfield, Sichuan Basin

In the course of completion of an ultra-deep well newly drilled in the Yuanba Gasfield, Sichuan Basin, long-section and large-scale deformation occurred in the heavy casing section and nickel base alloy casing section of the sealing Triassic limestone interval, so a new hole had to be sidetracked, which impels us to rediscover the applicability of conventional drilling and completion technology in ultra-deep wells. In this paper, based on the borehole condition and field operation data of this well, the borehole pressure field variation initiated by lost circulation in the low-pressure formation was analyzed from the perspective of dynamics, then, the variation pattern of differential pressure inside and outside the well bore at different time intervals was depicted, and the primary cause of such complication was theoretically revealed, i.e., the pressure wave generated by instant lost circulation in low-pressure formation would result in redistribution of pressure inside the downhole confined space, and then the crush of casing in the vicinity of local low-pressure areas. Pertinent proposals for avoiding these kinds of engineering complexities were put forward: ① when downhole sealing casing operation is conducted in open hole completion, liner completion or perforated hole, the potential damage of lost circulation to casing should be considered; ② the downhole sealing point and sealing mode should be selected cautiously: the sealing point had better be selected in the section with good cementing quality or as close to the casing shoe as possible, and the sealing mode can be either cement plug or mechanical bridge plug. This paper finally points out that good cementing quality plays an important role in preventing this type of casing deformation.

MECHANICAL AND MORPHOLOGICAL PROPERTIES OF POLYAMIDE 12 COMPOSITE FOR POTENTIAL BIOMEDICAL IMPLANT: INJECTION MOLDING AND DESKTOP 3D PRINTER

Fused filament fabrication is a filament based rapid prototyping process, which offers the possibility of new polymer material for invention of biomedical implant. This study represents an investigation on a preparation and characterization of new polyamide 12 reinforced with 20 wt% of zirconium dioxide and hydroxyapatite by desktop 3D printer in comparison with conventional manufacturing method, injection molding. Polyamide 12 composite was compounded, pelletized and filament-extruded prior to apply to a 3D printer. Sample prototypes from the new polyamide composite have been successfully made and tested. Mechanical (flexural and impact) and morphological properties were evaluated and compared. From the results, the printed polyamide composite exhibited lower mechanical properties than injection molded due to the formation of porosity, laminate weakness and low pressure during printing. Although the mechanical properties of printed parts were lower than molded parts, but the capability of 3D printer to fabricate any customized 3D object could lead to the bright future and great contribution in this area, while at the same time many improvements can be made for the future works.

Flow Analysis on Formation of Back-pressure in Exhaust System Applying Electronic-variable Valve

In the present study, the Conducting copy device was made as considering the position of electronic-variable valves in the exhaust system. Using the device, which was made to be similar to an actual engine, basic testing was conducted. Based on these results, ANSYS analysis was performed. As for the analysis method, 5 angle variables for opening angle and 6 flow variables were used. As for analysis conditions, analysis was conducted based on the data from the basic testing. For increased precision of results, analysis was repeated 5 times. Results of analysis according to the opening angle of the valve showed that the maximum pressure range and maximum velocity around the valve increased with the angle. Also, analysis according to flow showed that maximum pressure range increased with flow, and formation of low pressure behind the valve due to development of flow was pronounced. Therefore, through the present study, it was concluded that the angle or exhaust flow of electronic-variable valves impact the formation of bask pressure in exhaust systems.

Automatic detection of formations using images of oil well drilling cuttings

Abstract In oil well drilling process, a perennial issue is formations detection particularly in passing through high and low pressure formations. However, automatic classification of keybeds in the Gachsaran and Asmari formations by applying drill cutting images can help in decision-making, especially in oil wells of Iran, about mud weight and casing design for oil well drilling process. First, this study focuses on color analysis and fuzzy c-mean clustering to extract relevant features from images of the drill cuttings. Furthermore, a support vector machine and different kernel functions are utilized to classify the samples into different keybeds. Second, due to changing color of drilling cutting in each well, this study proposes texture analysis for keybeds classification. In this method, a co-occurrence matrix and features of energy, homogeneity, entropy and brightness are applied as feature vectors and classification is done by using the support vector machine too. This study, moreover, introduces the accuracy and response speed of the above techniques. To sum up, the results show that this method can be used to detect different formations (particularly between Gachsaran and Asmari) by approximately 95% accuracy.

Extreme Deepwater Wells Push Drillers to Begin Using Managed-Pressure Methods

Dual-Gradient Drilling Dual-gradient drilling has long been described as the drilling method of the future for challenging offshore wells. Now there are indications that it could start being used with some regularity, with multiple-well campaigns possible as early as next year. This method of managed-pressure drilling has been used a handful of times on a floating drilling rig, mostly to precisely manage the pressure in wells while drilling in weak, low-pressure formations prone to major fluid losses. Currently, Chevron and Statoil are seeking to use the system for deep, difficult, high-pressure formations in the US Gulf of Mexico. A drillship leased by Chevron, Pacific Santa Ana, is testing dual-gradient equipment on the ocean bottom while drilling a conventional well, and the company has leased a second drillship from Pacific Drilling, Pacific Sharav, that was built to accommodate dual-gradient drilling equipment. Statoil is seeking a permit to drill what could be the first dual-gradient well in the deep waters of the Gulf of Mexico, using another version of the managed-pressure method. “When we came here to the Gulf of Mexico, it was a perfect match with the challenges we had here,” said Uno Holm Rognli, vice president of drilling and wells in the offshore US for Statoil. “We started a program locally to develop this system” for conditions in the Gulf. It is the next step for the method used by Statoil off Norway, and by three companies in water 7,500 ft deep off Cuba. In both places it was used to successfully drill wells where pressure was so low, and the rock so fragile, that wells drilled using conventional methods were plagued by major fluid losses. While a few pioneers are working on dual-gradient drilling, there is a broader, growing base of operators using managed-pressure systems offshore. These are closed-loop systems with metering to allow precise measurement of change in fluid flows and chokes that allow them to apply backpressure when needed. Petronas and Petrobras are embracing managed-pressure drilling to deal with offshore wells where total fluid loss makes some wells impossible to drill using conventional methods. Managed-pressure equipment allows them to drill through sections of wells with cavernous underground hazards that can cause major fluid loss by using managed-pressure methods such as mud-cap drilling. ’New Ways To Manage Pressure Raise Well Control Questions’ When discussing dual-gradient drilling, there is an important distinction between controlling wells and well control. Controlling wells requires maintaining the balance between preventing influxes that could lead to trouble and exceeding the limit that could push drilling fluids out of the well and into the formation. Well control refers to the hardware, procedures, and training associated with dealing with situations in which an influx has occurred and needs to be quickly stopped before it grows into a bigger problem, and then circulated out of the well. For companies seeking to win approval from the US Bureau of Safety and Environmental Enforcement (BSEE) to drill the first deepwater well in the US Gulf of Mexico using dual-gradient drilling, questions about well control are critical. Offshore regulators want to be sure that all the new equipment has been thoroughly tested because this is a new way to drill, and the BSEE wants to be sure that it is understood that when it comes to well control, the requirements are not changing. “With Dual-Gradient Drilling, the Name Requires Explanation” Dual-gradient drilling covers a variety of methods for managing pressure within an offshore well while drilling. Dual refers to systems built to reduce or eliminate the pressure added by drilling fluid in the riser. The goal is to create distinct pressure gradients above and below the mudline. It is a departure from the simpler traditional approach using a single fluid combining water or oil plus drilling mud to make it viscous enough to remove cuttings while drilling, and just heavy enough to control pressures in the open hole without causing damage. As drilling moved into deeper waters the gap has narrowed between the effective mud weight-per-gallon to offset the formation pressure, and the level that can fracture it. Drillers refer to this slim margin as working within tight drilling windows.

Study of Low Density and High Strength Slag MTC System

With the demand of improving the second interfacial bonding strength and environmental protection, MTC cementing technology has obvious technical and economic advantages. However, due to containing lots of low-density materials and slurry treating agents, which make low strength, the application of low-density slag MTC cementing slurry system is restricted in the cementing of deep wells and low-pressure leakiness formations. According to the theory of particle distribution and based on particle size analysis of floating bead, micro silicon and slag, solid-phase proportioning design of low-density (1.35~1.55 g/cm3) slag MTC was carried out in this paper. By adjusting the adding amount of micro silicon and activators, the slag MTC cementing fluid system with the 24-hour compressive strength greater than 21.6MPa which has the density range of 1.35 to 1.55g/cm3 was get. This system has small initial consistency, short thickening transition time, low water loss and good rheological property. And at last, the mechanism of improving the strength of low-density slag MTC cementing fluid system was analyzed.

The Log Interpretation Analysis of the Block A in the South of the Fergana Basin

Fergana Basin, Central Asia's oldest oil and gas exploration area, reached an output of approximately 1.5 million tons per year in 1950s.【1,2】. Even after years of exploration and development, there is still a great resource potential【3】The exploration of block A in the south of the Fergana basin was started in 1930s suspended when the USSR collapsed. It was resumed in 2011 after it was acquired by company Z. There are some problems for the log interpretation such as the lack of related data, the low formation pressure caused by excessive exploration,. These problems cause the decline in terms of similarity between the log interpretation and the testing data. Based on the above issues, this paper studies the analysis of the problems and put forward reasonable proposals to the next step of the work to provide a sound basis for further exploration.

Influence of Engineering Pressure on Testing String Deformation

During well testing, liquid pressures exerted on testing string change frequently. Actions of downhole tools rely on annular or tubing pressure operation; information collection of the reservoir needs the production control valve switch on and off repeatedly. Pressure variability makes it very difficult to predict testing string safety both in deformation and strength. Although many measures have been taken to forecast pressure and component of the reservoir, exceptions often occur, and one exception is abnormal pressure. Considering technological process, axial deformation, helical buckling and strength of testing string are calculated with abnormal high and low formation pressure. Influence of other parameters is discussed, including string structure, completion fluid density, cushion and downhole tool operation pressures.

The Favorable Geological Conditions for Air Foam Drilling

Air foam drilling is adopted generally for its high rate of penetration, lower pollution to the reservoirs and low costs. Only when there are low formation pressure, long interval favorable formation, clear non-gas or non-oil formation and lower pay zone, air foam drilling can realize its advantages including maximum increasing rate of penetration, protecting reservoir and lowing the cost.

国際陸上科学掘削超高温地熱掘削プロジェクトJBBPの実現に向けた技術開発

An ICDP workshop proposal “Japan Beyond-Brittle Project (JBBP)” submitted by geothermal researchers mainly in Japanese and other countries was accepted by ICDP (International Continental Scientific Drilling Program) in 2012. The purpose of the scientific drilling project is to demonstrate the feasibility of a new concept of engineered geothermal system (EGS) in ductile formation zone. The target conditions of the JBBP well drilling are 3 to 5 km vertical depth, 350 to 500 °C estimated reservoir temperature, and 30 to 50 MPa estimated reservoir pressure. In this report, the author introduces the project outline, and discusses the technical problems relevant to drilling and completion such as extreme high temperature, hard and abrasive formation, low formation pressure and frequent risks of lost circulation, and HCl-H2S-CO2 coexisting low pH corrosive environment.

Пути повышения эффективности буровых работ в условиях аномально низких пластовых давлений

Пути повышения эффективности буровых работ в условиях аномально низких пластовых давлений

Transport mechanism of desorbed gas in coalbed methane reservoirs

Abstract The gas-liquid two-phase flow and mass transfer principle shows that the diffusion caused by concentration difference only happens in a single-phase fluid; gas-liquid two-phase diffluent solution happens in the way of dissolution; and gas-liquid two-phase insoluble or semi- soluble solution flows under differential pressure driving. These facts demonstrate that the transport of desorbed gas through matrix pores is the flow, and it doesn't conform to Fick law. The dissolution, diffusion, nucleation and bubble processes of desorbed gas through depressurization are studied, and the nonlinear flow model of free gas from matrix pores to the cleat and fracture system is established based on force analyses of the gas bubble and the gas column. Research shows that a small amount of desorbed gas diffuses by dissolution; most of them becomes nucleation and bubble, and then flows to the coal cleat and fracture system under the pressure difference driving; considering the existence of the pressure difference between the matrix pores and cleats, the pressure in coal matrix will reduce more slowly, the investigated radius will be shorter, and the outflow lag phenomenon of desorbed gas will appear. The dynamic reserve should be calculated not by using cleat pressure but by the pressure in coal matrix. The mechanism of enhanced methane recovery by CO2 injection is not only replacement but displacement. Improved methane recovery can be obtained by optimizing the production pressure difference, it is not reasonable that the lower formation pressure gives higher methane recovery.

A Multifunctional Drilling Fluid for Coalbed Methane Drilling

With extremely complicated geological conditions, there is abundant coalbed methane in the China's Ordos Basin Area. As a result of coexistence of different pressure systems in the same one naked well section, there are so many problems taking place occasionally during the drilling process, such as the formation lost circulation and collapse, which require the drilling fluid with a perfect rheology behavior and inhibitive to improve the well-bore containment. The coalbed methane well completions are diverse, usually including vertical well, horizontal well, multi-branch well, and other different well types. So the drilling fluid must have cuttings carried effectively and protect formation damaged to ensure that the process of drilling is security and smooth. Lots of drilling methods are used in the coalbed methane drilling, besides normal nearly balanced drilling, the under balance drilling fluids such as the air, fog, foam, etc particularly improved. All this drilling fluids require itself working compatibility with other fluids in the hole. Therefore, the special state-funded science and technology project has developed a novel bionic Fuzzy-Ball drilling fluid to meet the coalbed methane. Without additional equipments, this novel drilling fluids can be made, with non-solid phase and low density, 0.8~1.0 g/cm3. The inert solids can also be used to adjust the property to more than 1.0g/cm3, matching the near/under-balanced drilling. The formation well-bore containment can effectively improve to meet to the more than 1000 meters coalbed methane drilling in the open or low pressure formation, To portable cuttings effectively under low rate, the ratio of yield point and plastic viscosity can be adjusted to 1.0Pa/mPa•s or more. Combined with the air drilling, this novel Fuzzy-Ball material could not be converted to fluid to solve the formation water production, cavings, completion and other operations. 10 wells application of using the Fuzzy-Ball drilling fluid to complete the coal bed methane wells overcoming water production, collapse, lost circulation and air drilling etc, taking five branches well FL-H2-L, "U" horizontal well DFS-02-H2, water production and collapse well J35, air drilling CLY22 for examples, are introduced to indicate the bionic Fuzzy-Ball fluid application on the coalbed methane drilling spot.

A Multifunctional Drilling Fluid for Coalbed Methane Drilling

With extremely complicated geological conditions, there is abundant coalbed methane in the China's Ordos Basin Area. As a result of coexistence of different pressure systems in the same one naked well section, there are so many problems taking place occasionally during the drilling process, such as the formation lost circulation and collapse, which require the drilling fluid with a perfect rheology behavior and inhibitive to improve the well-bore containment. The coalbed methane well completions are diverse, usually including vertical well, horizontal well, multi-branch well, and other different well types. So the drilling fluid must have cuttings carried effectively and protect formation damaged to ensure that the process of drilling is security and smooth. Lots of drilling methods are used in the coalbed methane drilling, besides normal nearly balanced drilling, the under balance drilling fluids such as the air, fog, foam, etc particularly improved. All this drilling fluids require itself working compatibility with other fluids in the hole. Therefore, the special state-funded science and technology project has developed a novel bionic Fuzzy-Ball drilling fluid to meet the coalbed methane. Without additional equipments, this novel drilling fluids can be made, with non-solid phase and low density, 0.8~1.0 g/cm3. The inert solids can also be used to adjust the property to more than 1.0g/cm3, matching the near/under-balanced drilling. The formation well-bore containment can effectively improve to meet to the more than 1000 meters coalbed methane drilling in the open or low pressure formation, To portable cuttings effectively under low rate, the ratio of yield point and plastic viscosity can be adjusted to 1.0Pa/mPa•s or more. Combined with the air drilling, this novel Fuzzy-Ball material could not be converted to fluid to solve the formation water production, cavings, completion and other operations. 10 wells application of using the Fuzzy-Ball drilling fluid to complete the coal bed methane wells overcoming water production, collapse, lost circulation and air drilling etc, taking five branches well FL-H2-L, "U" horizontal well DFS-02-H2, water production and collapse well J35, air drilling CLY22 for examples, are introduced to indicate the bionic Fuzzy-Ball fluid application on the coalbed methane drilling spot.

Обоснование применения и исследование составов газожидкостных смесей для промывки скважин в условиях аномально низких пластовых давлений

Обоснование применения и исследование составов газожидкостных смесей для промывки скважин в условиях аномально низких пластовых давлений

Dissociation of methane under high pressure

Methane is an extremely important energy source with a great abundance in nature and plays a significant role in planetary physics, being one of the major constituents of giant planets Uranus and Neptune. The stable crystal forms of methane under extreme conditions are of great fundamental interest. Using the ab initio evolutionary algorithm for crystal structure prediction, we found three novel insulating molecular structures with P2(1)2(1)2(1), Pnma, and Cmcm space groups. Remarkably, under high pressure, methane becomes unstable and dissociates into ethane (C(2)H(6)) at 95 GPa, butane (C(4)H(10)) at 158 GPa, and further, carbon (diamond) and hydrogen above 287 GPa at zero temperature. We have computed the pressure-temperature phase diagram, which sheds light into the seemingly conflicting observations of the unusually low formation pressure of diamond at high temperature and the failure of experimental observation of dissociation at room temperature. Our results support the idea of diamond formation in the interiors of giant planets such as Neptune.

Characteristics of Abnormal Pressure Systems and Their Responses of Fluid in Huatugou Oil Field, Qaidam Basin

Abstract:Based on the comprehensive study of core samples, well testing data, and reservoir fluid properties, the construction and the distribution of the abnormal pressure systems of the Huatugou oil field in Qaidam Basin are discussed. The correlation between the pressure systems and hydrocarbon accumulation is addressed by analyzing the corresponding fluid characteristics. The results show that the Huatugou oil field as a whole has low formation pressure and low fluid energy; therefore, the hydrocarbons are hard to migrate, which facilitates the forming of primary reservoirs. The study reservoirs, located at the Xiayoushashan Formation (N21) and the Shangganchaigou Formation (N1) are relatively shallow and have medium porosity and low permeability. They are abnormal low‐pressure reservoirs with an average formation pressure coefficient of 0.61 and 0.72 respectively. According to the pressure coefficient and geothermal anomaly, the N1 and N21 Formations belong to two independent temperature‐pressure systems, and the former has slightly higher energy. The low‐pressure compartments consist of a distal bar as the main body, prodelta mud as the top boundary, and shore and shallow lake mud or algal mound as the bottom boundary. They are vertically overlapped and horizontally paralleled. The formation water is abundant in the Cl− ion and can be categorized as CaCl2 type with high salinity, which indicates that the abnormal low‐pressure compartments are in good sealing condition and beneficial for oil and gas accumulation and preservation.

Prediction of reservoir depletion degree and production GOR using logging-while-drilling data

Abstract Data of logging-while-drilling (LWD) log, formation pressure from MDT (modular formation dynamics tester) measurement, and production performance are used to study the relationship between depletion degree (formation pressure), initial production GOR (gas oil ratio) of single well and LWD response of depletion development in reservoirs. The results indicate that the overlap between density and neutron porosity curves from LWD data are related to reservoir depletion degree and production GOR when the formation pressure is less than the bubble point pressure. Larger overlap between the two curves corresponds to lower formation pressure and higher GOR. The relationship between the formation pressure, production GOR and porosity difference between density and neutron porosities can be derived from multi-analysis and regression. Through the analysis of the actual data from Block II of DLL Oilfield, empirical formulas have been established to predict formation pressure and production GOR from the porosity difference between density and neutron porosities. The predicted results correspond with MDT measurements and production GOR data, which proves the high reliability of the methods.