Tengfei Sun

Application of an Artificial Fish Swarm Algorithm in Solving Multiobjective Trajectory Optimization Problems

Drilling faces many complex design and multiobjective optimization problems. Solving these problems is also a critical and complicated part of drilling optimization as part of well trajectory design and optimization. Many researchers have developed many algorithms, but they have some disadvantages. We take the shortest total borehole length, the highest target shooting accuracy, the lowest cost, and the minimum friction as the multiobjective function, and we use a fish swarm algorithm for trajectory optimization. In this paper, we present the idea of using a nondominant relation for sorting in the algorithm and we also use an optimization program in the Matlab software to obtain all numerical solutions satisfying the constraints. Therefore it is quite adaptable for introducing the idea of nondominant sorting into appropriate multiobjective optimization problems based on a fish swarm algorithm. We give an example of the calculation, and also show that the algorithm and the calculation procedure are accurate and reliable. The algorithm has a simple structure, a small number of calculations, and good convergence.

Numerical Model for Evaluating Well Kick and Lost Circulation During Managed Pressure Drilling

Based on the rapidly varying casing pressure method and multiphase flow theory, we have constructed a transient mathematical model for managed pressure drilling (MPD) that combines kick with mud loss in a single fracture. The finite difference method was used to iteratively solve this model. The model calculated values agree well with the experimental results, which confirms the reliability of the model. Casing pressure, casing shoe pressure, pit gain, outlet flow, and choke opening during the entire well control process are analyzed. Experimental results show that equality of inlet flow and outlet flow may not imply influx stoppage when a kick is coupled with mud loss. In addition, the loss rate at the casing shoe initially increases linearly over time and then decreases exponentially, ultimately becoming constant. After completion of well control, drilling can be safely continued until loss is negligible. This study may provide a theoretical basis for better control of wells with complicated kick and circulation loss in managed pressure drilling (MPD).

Calculation of Equivalent Circulating Density and Solids Concentration in the Annular Space when Reaming the Hole in Deepwater Drilling

We propose a method for calculating the cuttings (solids) concentration in the annular space and the equivalent circulating density (ECD) in deepwater drilling, both in the pilot hole drilling step and in the reaming step. We have found that drilling a pilot hole followed by reaming has certain advantages over drilling with no pilot hole. When using technology involving preliminary drilling of a pilot hole, the solids concentration in the annular space and the equivalent circulating density are reduced.

Practical Application of a Combination of Principal Component Analysis and Cluster Analysis to Evaluate the Parameters of Layered Heterogeneous Formations in Dagang Oil Field

We take five parameters describing the properties of rocks (drillability, abrasive resistance, hardness, plasticity, and compressive strength) as the initial factors used for principal component analysis. Using this method, we obtained two principal components and composite scores, which we then treated using cluster analysis. These operations allow us to make a comprehensive evaluation of all 20 strata in the Dagang oil field (China). The results show that the 20 strata can be divided into four groups, which can provide a basis for drill bit selection and drilling design in the Dagang oil field.

Reliability Analysis of Annular Blowout Preventer Based on Fuzzy Relation Analysis

This paper considers application of the fault tree method to analyze types and reasons for failure of an annular blowout preventer (BOP). In combination with fuzzy relation analysis theory, we have calculated the fuzzy importance of basic events which can lead to failure plus the correlation coefficient for the minimum cut sets. Consequently, we can obtain the degree of correlation between the top event and the minimum cut sets. We have determined the key factors influencing stable operation of the annular BOP. Our results can provide a theoretical basis for use and improvement of an annular BOP.

Oil Reservoir Sensitivities to Various Exposures

The properties of Hongnan 2 block T1 oil reservoir in Xinjiang oilfield were analyzed in terms of petrological characteristics, rock granularity, clay composition, and other aspects. Experiments based on these results studied the sensitivities of the reservoir to velocity, acidity, alkalinity, stress, and water. The results showed moderate velocity sensitivity damage with an index in the range 42-56% and a critical flow velocity in the range 0.25-0.30 mL/min. Moderate and strong water sensitivities with indices varying from 52 to 65% and critical salinities from 5,000 to 10,000 mg/L were found. Water injected into a well should have salinity ≥ 10,000 mg/L to avoid water sensitivity damage. Weak sensitivity to alkalinity with an index varying from 31 to 36% with a critical pH of 8 was observed. Moderate and strong sensitivity to acidity was found for HCl fluid (15%); extremely strong, HCl (12%) + HF (3%); extremely strong, HCl (10%) + HF (3%) + HBF4 (8%); and no sensitivity, HCl (10%) + HBF4 (8%). The reservoir could be acidified by using HCl (10%) + HBF4 (8%). Significant changes in the reservoir core structure were not observed with large pressure differences. The critical pressure varied from 2 to 3.5 MPa. The permeability damage rate ranged from 13.33 to 18.68%. The stress sensitivity was weak.

Study of Drillability Evaluation in Deep Formations Using the Kriging Interpolation Method

During development of production processes in deep formations by means of wells placed in lower productive intervals, it is specifically such formations that have gradually become the major challenge in oil production. Due to the considerable depths and the combination of complex properties of the formations, in order for formulate a rational development program for the formations we need comprehensive understanding of their drillability and distribution in the specified region. In this paper; in order to provide such geological information, based on laboratory core experiments we have established the drillability of sections of the formation in a specified region by interpolation of support vectors by the kriging method.

Laboratory Studies of Fracture Geometry in Multistage Hydraulic Fracturing Under Triaxial Stresses

We present the results of a laboratory experiment on multistage hydraulic fracturing using a gel solution as the fracturing fluid, utilizing a laboratory setup for simulating hydraulic fracturing under triaxial stresses. As a result of the experiment, a fracture network was formed in a cubic rock specimen. We found that an almost planar fracture was formed during the first fracturing stage, while a concave (bowl-shaped) fracture was formed during the second stage. Interaction between the stress fields created by the two main hydraulic fractures (stress interference) caused growth of secondary cracks parallel to the simulated wellbore, but in this case led to a decrease in the width of the subsequent main fracture. We established that the penny-shaped fracture model is more suitable for predicting the geometry of hydraulic fractures in horizontal wells than two-dimensional (rectangular) fracture propagation models (the Perkins – Kern – Nordgren (PKN) model, the Khristianovic – Geertsma – de Klerk (KGD) model). Special attention needs to be paid to fracture spacing design in multistage hydraulic fracturing in horizontal wells.

Strain-Based Replacement Criterion for Third-Party Damaged Oil and Gas Pipelines

One reason for unpredictable failures in pipeline operation is third-party damage (TPD), which can occur due to actions of any third parties other than pipeline staff. Based on nonlinear dynamics theory, we propose a finite-element model for impact between an excavator bucket and the pipeline surface. The simulation was done for the following situations: gas transportation, bucket tooth striking the pipeline, bucket tooth separating from the pipeline, and unloading the pipeline pressure. We analyzed the pipeline damage mechanism and established the influence of the dent depth on residual strain and residual stress. Comparison of finite-element results with the standard criteria described in the standard ASME B31.8 showed that the latter criteria have a number of disadvantages.

Design and Field Testing of a Nitrogen Circulation Drilling System

In the recent decades, the merit of enhancing drilling rate by wellbore gas scavenging has been described comprehensively in many papers. This method began to be used widely and successfully in field conditions. In comparison with air and natural gas, due to its inertness and inflammability, gaseous nitrogen has become the most preferred fluid for drilling. The biggest shortcoming of using nitrogen gas as drilling fluid is high cost of its production. If the nitrogen gas circulated out of the wellbore could be recycled by some ground-based equipment and injected into the wellbore again, nitrogen gas drilling may become more viable. In this work, we developed a new nitrogen gas circulation drilling technology and carried out a systematic study of the proposed project, namely, the technological process, development of separation equipment and control system, etc. To verify the feasibility of this technological system, a comprehensive on-site experiment was designed and implemented for testing the prototype system.