Analysis of the Formation Mechanism of Crack Network in Shale by CT

During the drilling process of shale gas horizontal well, wellbore instability problem happens frequently. Especially in the horizontal interval, shale which has high levels of gamma is more likely to collapse which lead to delays, and exist certainly collapse period. The development of shale gas is restricted seriously. Research on the formation process of cracks network around the wellbore by CT chromatographic technique. The result reveals that under the condition of uniaxial compression, the cracks initiated inside the shale formation around the wellbore, with the propagation of cracks, between the orientation of cracks and the maximum stress direction will emerge a certain deviated angle. The drilling fluid filtrates into the formation and reduce the strength of rock which will prompt crack propagation and form crack network. Finally the wellbore will collapse with drilling fluid continuous invasion, because the invasion have altered the stress intensity factor at fracture tip, and changed the propagating direction of crack and the friction coefficient of fracture plane, which will reduce the strength of rock and the effective stress of the rock around the wellbore. Crack network dominates the mechanism of instability; mud weight increases do not necessarily lead to a more stable borehole and can further destabilize the wellbore.

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Experimental study of Zubair shale stability of east Baghdad oil field using different additives in water based mud

Journal of Petroleum Exploration and Production Technology ◽

10.1007/s13202-019-00820-4 ◽

2019 ◽

Vol 10 (3) ◽

pp. 1215-1225

Author(s):

Asawer A. Alwassiti ◽

Mayssaa Ali AL-Bidry ◽

Khalid Mohammed

Keyword(s):

Drilling Fluid ◽

Oil Field ◽

Oil Fields ◽

Drilling Fluids ◽

Fluid Type ◽

Wellbore Instability ◽

Immersion Period ◽

Shale Formation ◽

Shale Recovery ◽

Polymer Type

AbstractShale formation is represented as one of the challenge formations during drilling wells because it is a strong potential for wellbore instability. Zubair formation in Iraqi oil fields (East Baghdad) is located at a depth from 3044.3 to 3444 m. It is considered as one of the most problematic formations through drilling wells in East Baghdad. Most problems of Zubair shale are swelling, sloughing, caving, cementing problem and casing landing problem caused by the interaction of drilling fluid with the formation. An attempt to solve the cause of these problems has been adapted in this paper by enhancing the shale stability through adding additives to the drilling fluid. The study includes experiments by using two types of drilling fluids, API and polymer type, with five types of additives (KCl, NaCl, CaCl2, Na2SiO3 and Flodrill PAM 1040) in different concentrations (0.5, 1, 5 and 10) wt% and different immersion period (1, 24 and 72 h) hours. The effect of drilling fluids and additive salts on shale has been studied by using different techniques: (XRD, XRF, reflected and transmitted microscope) as well shale recovery. The results show that adding 10 wt% of Na2SiO3 to API drilling fluid results in a high percentage of shale recovery (78.22%), while the maximum shale recovery was (80.57%) in polymer drilling fluid type gained by adding 10 wt% of Na2SiO3.

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Oil-Based Drilling Fluid Plugging Method for Strengthening Wellbore Stability of Shale Gas

Geofluids ◽

10.1155/2021/6674574 ◽

2021 ◽

Vol 2021 ◽

pp. 1-13

Author(s):

Pengcheng Wu ◽

Chengxu Zhong ◽

Zhengtao Li ◽

Zhen Zhang ◽

Zhiyuan Wang ◽

...

Keyword(s):

Shale Gas ◽

Drilling Fluid ◽

Wellbore Stability ◽

Drilling Fluids ◽

Fluid System ◽

Horizontal Drilling ◽

Wellbore Instability ◽

Filtration Loss ◽

Treatment Agent ◽

Stability Method

Finding out the reasons for wellbore instability in the Longmaxi Formation and Wufeng Formation and putting forward drilling fluid technical countermeasures to strengthen and stabilize the wellbore are very crucial to horizontal drilling. Based on X-ray diffraction, electron microscope scanning, linear swelling experiment, and hot-rolling dispersion experiment, the physicochemical mechanism of wellbore instability in complex strata was revealed, and thus, the coordinated wellbore stability method can be put forward, which is “strengthening plugging of micropores, inhibiting filtrate invasion, and retarding pressure transmission.” Using a sand bed filtration tester, high-temperature and high-pressure plugging simulation experimental device, and microporous membrane and other experimental devices, the oil-based drilling fluid treatment agent was researched and selected, and a set of an enhanced plugging drilling fluid system suitable for shale gas horizontal well was constructed. Its temperature resistance is 135°C and it has preferable contamination resistibility (10% NaCl, 1% CaCl2, and 8% poor clay). The bearing capacity of a 400 μm fracture is 5 MPa, and the filtration loss of 0.22 μm and 0.45 μm microporous membranes is zero. Compared with previous field drilling fluids, the constructed oil-based drilling fluid system has a greatly improved plugging ability and excellent performance in other aspects.

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New insight on studying the effect of both chemical sensitivity and rock mechanical properties in shale formation to minimize wellbore instability problems

E3S Web of Conferences ◽

10.1051/e3sconf/202020503012 ◽

2020 ◽

Vol 205 ◽

pp. 03012

Author(s):

Mohammad H. Alqam ◽

Hazim H. Abass ◽

Abdullah M. Shebatalhmad

Keyword(s):

Drilling Fluid ◽

Wellbore Stability ◽

High Porosity ◽

Shale Formations ◽

Wellbore Instability ◽

Testing Procedures ◽

Shale Formation ◽

Rock Mechanical Properties ◽

Core Volume ◽

Shale Permeability

Historically, many of the wells drilled in in shale formations have experienced a significant rig downtime due to wellbore instabilities. Most of the instability problems originated from the encountered shale formations. The objectives of this study include (1) to measure the properties governing shale strength and drilling fluid/shale interaction, and (2) to establish a reliable and efficient rock mechanical testing procedures related to wellbore stability. Preserved shale core has been recovered from shale formation and special core handling procedure was implemented. Mineral oil was used for plugging and core preservation. Rock mechanical characterization was conducted on core samples using both XRD/SEM techniques to study the core mineralogy. In addition, shale permeability was determined by two methods: flow testing and pressure transition methods. The results indicated that shale has high percentage of quartz (30-40%) which causes the shale to have high porosity and high permeability. The unconfined compressive strength of shale is very low which any drilling fluid that contains water phase further reduces. The Young’s modulus is very low which makes near wellbore deformation high. Based on the shale swelling testing, the all-oil fluid show no volume change occurred to the shale. When the same shale was exposed to the 7% KCl, about 16% increase in core volume occurred in 48 hours. This means that all samples allowed the water to flow into the shale formation.

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Borehole Stability in Shale Formation: Modeling the Effects of Molecular Weight and Concentration of Polymers in the Drilling Fluids Formulation

Journal of Petroleum Research and Studies ◽

10.52716/jprs.v5i1.143 ◽

2014 ◽

Vol 5 (1) ◽

pp. 260-270

Author(s):

Khoshniyat A ◽

Shojaei M. ◽

Jarahian K. ◽

Mirali M. ◽

Ghorashi S. ◽

...

Keyword(s):

Molecular Weight ◽

Reflection Coefficient ◽

Drilling Fluid ◽

Exchange Capacity ◽

Oil Field ◽

Wellbore Stability ◽

Drilling Fluids ◽

Drilling Process ◽

Borehole Stability ◽

Shale Formation

A new experimental model was developed to predict the role of special polymeric additives, in the drilling fluid formulation, on the wellbore stability in shale formation. The shale formation was regarded as a non-ideal membrane and the effects of various characteristics of the added polymers were studied on the membrane reflection coefficient. The model was applied to unique field data from the oil field in south of Iran, including clay structure, cation exchange capacity (CEC), density and porosity of the shale. The results, using various polyglycols and polyacrylamides as the polymeric additive, showed that the structure of the polymeric chains e.g. type and content of ionic segments had significant effect on their adsorption mechanism and its strength. It was concluded that increasing the molecular weight of the polymer chains decreased the rate and amount of the adsorption due to the increasing of the entanglements between the chains which in turn limited their mobility. So, adsorption of the polymeric material on the shale had significant impress on its performance as a membrane by increasing the shale reflection coefficient enhancing its stability during drilling process. Finally, the developed model results were in good agreement by experimental test results which was done in a specific shale stability set up.

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Modeling of Filter Cake Composition in Maximum Reservoir Contact and Extended Reach Horizontal Wells in Sandstone Reservoirs

Journal of Energy Resources Technology ◽

10.1115/1.4035022 ◽

2016 ◽

Vol 139 (3) ◽

Cited By ~ 12

Author(s):

Mohamed Mahmoud ◽

Badr S. Bageri ◽

Salaheldin Elkatatny ◽

Saleh H. Al-Mutairi

Keyword(s):

Horizontal Well ◽

Filter Cake ◽

Drilling Fluid ◽

Material Balance ◽

Gas Production ◽

Circulation Rate ◽

Drilling Process ◽

Horizontal Section ◽

Rock Composition ◽

Sandstone Formation

Drilling mud should be properly designed to build an effective filter cake on the formation face during the drilling process. This filter cake should be removable to allow the oil and gas production. The need for removal increases when the liftoff pressure is high or when the formation drawdown is extremely low. An effective filter cake removal design includes the knowledge of the filter cake composition along the horizontal section. This paper, for the first time, introduces material balance model to predict the composition of the filter cake along the length of the lateral of an actual horizontal well drilled in a sandstone formation. The model is based on the material balance of two sources of solids: the first one is the drilling fluid solids and the second one is the drilled-formation solids. The mud used to drill the rock was contaminated by the drilled-formation solids. The parameters used to construct the model were composition of the mud and formation, efficiency of each separation stage, rate of penetration (ROP), and mud circulation rate. The model was validated with actual mud samples collected from different locations along the horizontal section of a sandstone formation. The model showed that the sand content in the filter cake is affected by ROP, rock composition, mud composition and volume, and efficiency of sand separation equipment. We came up with several correlations that can be used to design the drilling fluid operations in horizontal well to avoid the formation of irremovable filter cake.

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Integrated Workflow Solutions Deliver Breakthrough in Sichuan Shale Gas Drilling

10.2118/201043-ms ◽

2021 ◽

Author(s):

Wenzhe Li ◽

Liang Tang ◽

Ye Zhuang ◽

Lu Zhang ◽

Yifan Cai ◽

...

Keyword(s):

Shale Gas ◽

Average Rate ◽

Drilling Fluid ◽

Gas Production ◽

Mitigation Strategies ◽

Drilling Process ◽

Mountainous Regions ◽

Gas Drilling ◽

Geomechanical Analysis ◽

Delivery Efficiency

Abstract The Sichuan shale gas deposits are in remote, mountainous regions and the gas-bearing rocks are deep and in tectonically complicated areas. The plan to make shale gas account for more than 40% of the Chinese total natural gas production by 2040 requires shorter well delivery periods and higher well productions. It is therefore crucial to improve the overall drilling efficiency with the limited rig capability and geological challenges. To improve capital efficiency, a multi-disciplinary approach integrating subsurface understanding with well engineering and drilling practices was implemented. Central to this drilling optimization effort are risk mitigation strategies, utilizing solutions based on robust geomechanical understanding and critical drilling experience reviews, engineered to improve wellbore placement, drilling fluid formulation, and bit and BHA designs. A novel wellbore-strengthening oil-based mud system was implemented to maintain shale stability. A rotary steerable drilling system and reservoir navigation technology were deployed together with the application of specific poly-crystalline diamond compact (PDC) bit design. A new-generation advanced cuttings analysis method was also applied with the lithology, organic matter and fracability of rock could be evaluated in real time to assist the reservoir navigation during the drilling. This integrated solution was deployed in the drilling of 8 ½" holes of Changning Shale gas field. A cross-functional team was formed so that the operator, the drilling contractor and the service company can collaborate closely with expertise across multiple functions and disciplines. Suitable mud weight was provided by the detailed geomechanical analysis to account for the high pore pressure and near bed-parallel drilling conditions. To place the laterals in the thin targeted sub-layer with high TOC, a rotary steerable system (RSS) with azimuthal GR provide not only precise steering and directional controls, but also enable increased reservoir coverage by expanding the lateral section as well as drilling the build and horizontal sections in a single run without BHA trips. The combination of RSS with specialized bits as an optimized bit and BHA system maximizes the steering performance while delivering superior borehole quality by reducing drill string vibration and the minimizing mechanical specific energy, all of which contribute to the overall improvement in the well delivery efficiency. This integrated drilling solution has achieved remarkable results by doubling the average rate of penetration (ROP) to 15.5m/h compared to an offset well on the same pad of 7.4m/h. The well was placed successfully in the targeted zone with a 100% reservoir contact. And the total drilling time was shortened by 40% compared to similar wells nearby. The integrated solution has brought breakthrough to improve the well delivery efficiency in the China shale gas development. This paper describes the integrated workflow solutions and detailed technical optimizations of the 8 ½" section drilling process.

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A Systematic Approach to De-Risk and Improve Shale Gas Horizontal Well Drilling

10.2118/202119-ms ◽

2021 ◽

Author(s):

Xiang Gao ◽

Jiaxin Zeng ◽

Jiajun Xie ◽

Liang Tang ◽

Wenzhe Li ◽

...

Keyword(s):

Real Time ◽

Shale Gas ◽

Horizontal Well ◽

Risk Mitigation ◽

Effective Means ◽

Integrated Approach ◽

Gas Production ◽

Wellbore Stability ◽

Drilling Process ◽

Well Drilling

Abstract Horizontal well drilling contribute to a dramatic increase of shale gas production in unconventional reservoirs. However, the drilling is also risky and challenging with different types of drilling problems often encountered including stuck pipes, inflows, losses and pack-offs, etc. To reduce shale-gas development costs, shale gas operators are faced with finding effective solutions to minimize drilling risks and improve drilling efficiency. A holistic workflow, which can be divided into three steps: pre-drilled modelling and assessment, real-time monitoring, and post-drilled validation, is proposed. Based on the pre-drilled geomechanical modeling, mud weights, mud formulations and casing setting depths are optimized to ensure wellbore stability during the drilling process. Real-time operations involve monitoring drilling parameters and cavings characteristics (shape and volume), and providing updated recommendations for field drilling engineers to mitigate and reduce borehole instability related problems. During the post-drilled stage, the updated geomechanical model will be used for optimizing the drilling designs of upcoming wells. With geomechanics as foundation, a systematic workflow was developed to provide integrated solutions by using multiple technologies and services to reduce serious wellbore instability caused by abnormal formation pressures, wellbore collapse and other complex drilling problems. The implementation of the systematic and holistic workflow has proven to be extremely successful in supporting the drilling of shale gas wells in China. The integrated approach, which was applied in a Changning shale gas block in Sichuan Basin for the first time in March 2019, recorded an improvement in ROP by 111.2% and a reduction in mud losses by 89.9% compared with an offset well without the risk mitigation strategy applied in the same pad. The geomechanics-based approach provides a convenient and effective means to assist field engineers in mud weight optimization, drilling risk assessments, and horizontal well drilling performance evaluation. The approach can also be extended to reduce potential drilling risks and improve wellbore stability, all of which contributes to reducing drilling costs and optimizing subsequent massive hydraulic fracturing jobs.

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A Multifunctional Drilling Fluid for Coalbed Methane Drilling

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.455-456.1317 ◽

2012 ◽

Vol 455-456 ◽

pp. 1317-1323

Author(s):

Li Hui Zheng ◽

Ming Wei Zhang ◽

Yong Lin

Keyword(s):

Coalbed Methane ◽

Horizontal Well ◽

Drilling Fluid ◽

Drilling Fluids ◽

Drilling Process ◽

Water Production ◽

Well Bore ◽

Lost Circulation ◽

Geological Conditions ◽

Air 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.

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