The Effect of Shale Chemistry on Gas Production Decline in Hydraulically Fractured Shale Gas Wells

Producers have always been eager to know the reasons for the difference in the production of different shale gas wells. The Southern Sichuan Basin in China is one of the main production zones of Longmaxi shale gas, while the shale gas production is quite different in different shale gas wells. The Longmaxi formation was deposited in a deep water shelf that had poor circulation with the open ocean, and is composed of a variety of facies that are dominated by fine-grained (clay- to silt-size) particles with a varied organic matter distribution, causing heterogeneity of the shale gas concentration. According to the different mother debris and sedimentary environment, we recognized three general sedimentary subfacies and seven lithofacies on the basis of mineralogy, sedimentary texture and structures, biota and the logging response: (1) there are graptolite-rich shale facies, siliceous shale facies, calcareous shale facies, and a small amount of argillaceous limestone facies in the deep - water shelf in the Weiyuan area and graptolite-rich shale facies and carbonaceous shale facies in the Changning area; (2) there are argillaceous shale facies and argillaceous limestone facies in the semi - deep - water continental shelf of the Weiyuan area and silty shale facies in the Changning area; (3) argillaceous shale facies are mainly developed in the shallow muddy continental shelf in the Weiyuan area, while silty shale facies mainly developed in the shallow shelf in the Changning area. Judging from the biostratigraphy of graptolite, the sedimentary environment was different in different stages.

Download Full-text

Analysis of Fractured Sections in Shale Gas Wells Based on PCA - Logistic Regression Model

Materials Science Forum ◽

10.4028/www.scientific.net/msf.980.483 ◽

2020 ◽

Vol 980 ◽

pp. 483-492

Author(s):

Lei Ji ◽

Ju Hua Li ◽

Guan Qun Li ◽

Jia Lin Xiao ◽

Sean Unrau

Keyword(s):

Logistic Regression ◽

Shale Gas ◽

Logistic Regression Model ◽

Gas Production ◽

Gas Wells ◽

Gas Reservoirs ◽

Discriminant Model ◽

Economic Exploitation ◽

High Production ◽

Pca Algorithm

In order to optimize the layout and economic exploitation of horizontal fracturing wells and completion in shale gas reservoirs, we propose a model for evaluating shale gas fractured sections based on an improved principle component analysis (PCA) algorithm with logistic regression. The 229 gas production sections in 22 fractured shale gas wells in the main block of the Fuling Shale Development Demonstration Zone were selected, and PCA is used for dimensionalite reduction. According to the PCA results, 6 key parameters are chosen to determine the productivity of fractured wells. Taking the probability distribution of high production after fracturing as the research objective, a logistic regression discriminant model was constructed using the dichotomy method. The prediction results show that the model has 82.1% accuracy and is reliable. The model can be used to classify and gas wells to be fractured, and it provides guiding significance for reasonable optimization of well sections in the area selected for fracturing.

Download Full-text

Immediate Gas Production from Shale Gas Wells: A Two-Phase Flowback Model

10.2118/168982-ms ◽

2014 ◽

Cited By ~ 16

Author(s):

O.A. Adefidipe ◽

H. Dehghanpour ◽

C.J. Virues

Keyword(s):

Shale Gas ◽

Gas Production ◽

Gas Wells ◽

Two Phase

Download Full-text

Hydrodynamic Equilibrium Simulation and Shut-in Time Optimization for Hydraulically Fractured Shale Gas Wells

Energies ◽

10.3390/en13040961 ◽

2020 ◽

Vol 13 (4) ◽

pp. 961

Author(s):

Fei Wang ◽

Qiaoyun Chen ◽

Yingqi Ruan

Keyword(s):

Shale Gas ◽

Gas Production ◽

Fluid Loss ◽

Hydraulic Fractures ◽

Hydraulic Pressure ◽

Gas Wells ◽

Fracturing Fluid ◽

Equilibrium Time ◽

Chemical Osmosis ◽

Hydrodynamic Equilibrium

Post-fracturing well shut-in is traditionally due to the elastic closure of hydraulic fractures and proppant compaction. However, for shale gas wells, the extension of shut-in time may improve the post-fracturing gas production due to formation energy supplements by fracturing-fluid imbibition. This paper presents a methodology using numerical simulation to simulate the hydrodynamic equilibrium phenomenon of a hydraulically fractured shale gas reservoir, including matrix imbibition and fracture network crossflow, and further optimize the post-fracturing shut-in time. A mathematical model, which can describe the fracturing-fluid hydrodynamic transport during the shut-in process, and consider the distinguishing imbibition characteristics of a hydraulically fractured shale reservoir, i.e., hydraulic pressure, capillarity and chemical osmosis, is developed. The key concept, i.e., hydrodynamic equilibrium time, for optimizing the post-fracturing shut-in schedule, is proposed. The fracturing-fluid crossflow and imbibition profiles are simulated, which indicate the water discharging and sucking equilibrium process in the coupled fracture–matrix system. Based on the simulation, the hydrodynamic equilibrium time is calculated. The influences of hydraulic pressure difference, capillarity and chemical osmosis on imbibition volume, and hydrodynamic equilibrium time are also investigated. Finally, the optimal shut-in time is determined if the gas production rate is pursued and the fracturing-fluid loss is allowable. The proposed simulation method for determining the optimal shut-in time is meaningful to the post-fracturing shut-in schedule.

Download Full-text

Prediction of Shale-Gas Production at Duvernay Formation Using Deep-Learning Algorithm

SPE Journal ◽

10.2118/195698-pa ◽

2019 ◽

Vol 24 (06) ◽

pp. 2423-2437 ◽

Cited By ~ 11

Author(s):

Kyungbook Lee ◽

Jungtek Lim ◽

Daeung Yoon ◽

Hyungsik Jung

Keyword(s):

Time Series ◽

Shale Gas ◽

Transient Flow ◽

Time Series Data ◽

Gas Production ◽

Series Data ◽

Production Data ◽

Gas Wells ◽

Future Production ◽

Unseen Data

Summary Decline–curve analysis (DCA) is an easy and fast empirical regression method for predicting future well production. However, applying DCA to shale–gas wells is limited by long transient flow, a unique completion design, and high–density drilling. Recently, a long short-term-memory (LSTM) algorithm has been widely applied to the prediction of time–series data. Because shale–gas–production data are time–series data, the LSTM algorithm can be applied to predict future shale–gas production. After information for 332 shale–gas wells in Alberta, Canada, is obtained from a commercial database, the data are preprocessed in seven steps, including cutoffs for well list, data cleaning, feature extraction, train and test sets split, normalization, and sorting for input into the LSTM model. The LSTM model is trained in 405 seconds by two features of production data and a shut–in (SI) period from 300 wells. The two–feature case shows a better prediction accuracy than both the one–feature case (i.e., production data only) and the hyperbolic DCA, where the three methods are tested on unseen data from 15 wells. The two–feature case can predict future production rates according to the SI period and provide a stable result for available time–series data.

Download Full-text

Review of metering and gas measurements in high-volume shale gas wells

Journal of Petroleum Exploration and Production Technology ◽

10.1007/s13202-021-01395-9 ◽

2021 ◽

Author(s):

Yiming Zhang ◽

John Wang

Keyword(s):

Shale Gas ◽

Measurement Accuracy ◽

Low Cost ◽

High Volume ◽

Gas Production ◽

Lessons Learned ◽

Background Information ◽

Volumetric Measurement ◽

Gas Wells ◽

Gas Measurements

AbstractCoriolis, turbine, V-cone, and orifice meters have been used in measurement of gas production in shale wells. Flange-tapped concentric orifice meters are commonly used in measurement of shale gas production volumes due to their low cost, accuracy, and ease of maintenance compared to other types of meters. However, shale gas wells are producing at high flow rates, high pressure, and possibly gas compositions change, which might affect volumetric measurement accuracy that was developed for conventional gas wells. Thus, it is critical to investigate the metering and measurements technologies that are being applied in shale gas wells to further understand and improve the accuracy of gas volumetric measurements. This paper provides a comprehensive review and analysis of background information, design, measurement, and uncertainties associated with Coriolis meters, turbine meters, V-cone meters, and orifice meters. We also discussed the lessons learned through our field experiences in computing gas volumes using SCADA information in shale gas and conventional gas production.

Download Full-text

Impact of Casing Eccentricity on Cement Sheath

Energies ◽

10.3390/en11102557 ◽

2018 ◽

Vol 11 (10) ◽

pp. 2557 ◽

Cited By ~ 3

Author(s):

Kui Liu ◽

Deli Gao ◽

Arash Taleghani

Keyword(s):

Stress Distribution ◽

Shale Gas ◽

Radial Stress ◽

Circumferential Stress ◽

Horizontal Wells ◽

Gas Production ◽

Gas Wells ◽

Sustained Casing Pressure ◽

Cement Sheath ◽

Casing Pressure

Sustained casing pressure (SCP) in shale gas wells caused by cement sheath failure can have serious impacts on safe and efficient gas production. Considering the fact that horizontal wells are widely used for production from shale, the cementing quality and casing centricity is barely ensured in these wells. Among other indications, the casing eccentricity is identified very often in wells with SCP problems in the Sichuan field in China. Hence, the objective of this study is to analyze the effect of the casing eccentricity on the integrity of the cement sheath. To better understand stress distribution in eccentric cement sheaths, an analytical model is proposed in this paper. By comparing the results of this model with the one’s with centric casing, the impacts of the casing eccentricity on the integrity of the cement sheath is analyzed. During fracturing treatments, the casing eccentricity has a little effect on stress distribution in the cement sheath if the well is well cemented and bonded to the formation rock. However, on the contrary, the casing eccentricity may have serious effects on stress distribution if the cementing is done poorly. The debonding of casing–cement–formation interfaces can significantly increase the circumferential stress in the cement sheath. At the thin side of the cement sheath, the circumferential stress could be 2.5 times higher than the thick side. The offset magnitude of the casing eccentricity has little effect on the radial stress in the cement sheath but it can significantly increase the shear stress. We found that the risk of cement failure may be reduced by making the casing string more centralized, or increasing the thickness of the casing. The results provide insights for design practices which may lead to better integrity in shale gas wells.

Download Full-text