Estudo das características de empacotamento, fluidização e transporte pneumático de cascalhos da perfuração de poços de petróleo e gás

Abstract

The pneumatic conveying process of cuttings generated during the drilling of oil and gas wells is influenced by several factors associated with the characteristics of the material and operating conditions. The main objective of this thesis was to study the pneumatic conveying of drilling cuttings, in addition to investigating the ideal operating conditions, considering the effect of moisture on the material handling properties, the most adequate pneumatic conveying flow regime, and operational conditions for conveying. For this purpose, it was initially necessary to develop an accurate device to determine the bulk properties of fixed beds of granular materials. In addition, using this device, it was sought to evaluate the effect of the number, frequency, and amplitude of the taps of fixed beds packed with granular materials on the tapped bulk density results obtained. In a second moment, it was verified the influence of cuttings moisture content on the dynamics of aggregation/disaggregation of particles, bulk properties of fixed beds (measured with the developed device), flowability, fluidization characteristics, and de-aeration behavior. The properties obtained in these analyzes were called handling properties. Based on the data obtained, it was pursued to establish a classification of the different handling behaviors of cuttings according to the moisture content and to make predictions of the influence of moisture in the most suitable conveying flow regime. The results obtained showed that the developed device allowed the determination of loose and tapped bulk densities with high precision (0.002 g.cm-3) and accuracy (0.001 g.cm-3). In addition, the tapped bulk density was more influenced by the frequency and amplitude of the taps. Regarding the influence of moisture content on the drilling cuttings handling properties, the results allowed the identification of four characteristic states, named: dry (1.3-7.7%), aggregate (7.7-15.2%), disaggregate (15.2-27.6%), and slurry (27.6-44.0%). It is possible to notice that the increment of moisture up to 15.2% promoted the formation of looser interparticle structures, which showed less resistance to airflow. However, these structures were steadier, showing greater difficulty to flow, as well as, fluidizing and retaining air. The continuous increment of moisture beyond 15.2%, propitiated denser and more resistant to airflow interparticle structures. The material could flow more easily, retaining more air and being relatively easier to fluidize. The conveying flow regime predictions indicated that cuttings in dry and slurry states can be conveyed only in the lean phase, while those in aggregate/disaggregated state can be conveyed in the dense phase plug flow. In general, cuttings in the dry state showed good and stable handling properties as compared to other states, being desirable for cuttings handling operations. Finally, it was presented the process of design, construction, instrumentation, and control of a pneumatic conveying system in the dense and lean phase of industrial-scale for cuttings in the dry state. Then, the multiple regression technique linked to designed experiments was used to quantify the effects of air flows used for blow tank pressurization, material fluidization, and aeration of the discharged material, as well as the mass of material loaded in the blow tank, in the variables: discharge flow rate, average discharge pressure and pressure drop in the conveying line. The results obtained allowed mapping a wide operational range in which it was possible to pneumatically convey in the dense phase drilling cuttings in the dry state. It was also possible to identify the optimal operating points in which the discharge flow rates were high and the pressure drops in the conveying line were not excessive. In addition, the establishment of the state diagram, together with the analysis of the pressure signal in the conveying line as a function of time, allowed to infer about the most probable conveying regimes that took place during the experiments.