Fluid invasion into productive zones has been widely recognized as detrimental to well productivity. Filtrate and solids invasion can cause irreversible formation damage and permeability reduction. Drilling fluids are formulated to avoid excessive fluid penetration into productive zones. Non-damaging acid-soluble solids are usually added to drill-in fluids in order to promote pore plugging and minimize fluid penetration. Also specific polymers are used that reduce fluid invasion due to surface chemistry and viscosity effects. The development of less invasive non-damaging fluid formulations requires the knowledge of filtration mechanisms of solids containing polymeric solutions in porous media. The work was carried out in two ways: solids with different particle size distributions and concentrations were added to a polymeric base formulation and the filtration behavior of the fluids through unconsolidated porous media was evaluated using computer tomography scanning. Along with the solids investigation, different types of polymeric solutions exhibiting different shear and extensional rheological properties were tested using the same procedure and technique. The extent of the invaded zone could then be measured and the performance of the different types of material could be evaluated. The results from the lab tests will be used to support the development of a filtration model to calculate filtration flow rates and depth of penetration accounting for non-newtonian rheology and type of bridging agent on filtration mechanism. Introduction To better understand the relative importance of factors contributing to filtration, an extensive experimental work is required to support the development of a mathematical model to predict filtration rates and depth of penetration. The paper presents a methodology to evaluate filtration properties of drilling fluids through unconsolidated porous media. Results from static filtration experiments of polymeric fluid formulations are presented aiming: the development of a filtration model to calculate filtration flow rates and depth of penetration accounting for non-newtonian rheology and type of bridging agent on filtration mechanism; the evaluation of filtration characteristics of different fluid formulations; the effect of different polymers and bridging agents on filtration properties of fluids; the development of non-invasive fluid formulations. Background Theoretical and experimental studies on static and dynamic filtration of water based drilling fluids have been carried out to evaluate the effects of fluid type and pH, solids shape, size and concentration, pressure and shear rates on filtration properties of the fluids1. The inadequate control of fluid properties is usually associated with wellbore instability, excessive torque and drag, differential stuck pipe and formation damage2. Therefore, it is imperative to correctly estimate the filtration characteristics of the fluids during drilling and completion so as to properly diagnose and prevent the above-mentioned problems. Moreover, severe fluid losses experienced during drilling in ultra deep waters have brought the attention to the need for non-invasive fluids to guarantee a successful operation. One of the main problems related to the presence of filtrate in productive oil and gas zones is the significant permeability reduction and well productivity decrease. The modeling of filtration process as to predict permeability changes and depth of damage penetration into the productive zone is essential to establish the stimulation technique that will better remove the existing damage3.

The Congro field (Campos Basin, Brazil) contains considerable reserves located in a extremely heterogeneous, very low-permeability carbonate reservoir. For many years after its discovery, this reservoir was considered non-economic. However, a newly drilled horizontal well showed encouraging results. An advanced, integrated reservoir study showed that the exploitation of the reservoir can be economically attractive if non-conventional wells are used. In this work, we demonstrate how cutting-edge technology plus interdisciplinary efforts involving geophysics, geology, and reservoir engineering were the key to make a noneconomic asset into an economic one. Two major problems were faced: the short available time (only two months for the whole study) and the lack of data. The lack of data was overcome by using analogy with a similar, well-sampled reservoir. The time constraint was handled by taking an integrated approach where the geophysical, geological, and numerical simulation models were built almost simultaneously. Stochastic reservoir models were generated using a geostatistical method called truncated Gaussian technique to assess uncertainty on facies distribution. Three different types of wells were considered: vertical fractured, horizontal, and multilateral. As multilateral wells showed better economics, we optimized the number of legs and their length based on numerical simulation. Introduction Technology has more and more made the difference between success and failure of hydrocarbon exploitation projects, especially when the asset is on the economic borderline. New drilling techniques, as well as reservoir description techniques, have allowed the development of fields that had been considered economically unattractive in the past. Throughout the world, many projects have been reviewed and had their economic indicators (net present value, payout, etc.) significantly improved when new technologies were applied to them. Multilateral drilling and seismic interpretation are among the techniques that suffered major breakthroughs in the last few years. The first allows one to greatly improve well productivity index as well as enhance sweep efficiency; furthermore, the use of multilateral wells reduces drilling and equipment costs such as flowlines and christmas trees. The second can give a pretty good idea of where the best-quality rock facies are located and help identify reserves that may not be produced optimally. A third technique that can add value to a project is geostatistics. Multiple equiprobable reservoir models can be generated to assess uncertainty on reservoir description and on reservoir production forecast. Geostatistical models are generally more detailed than conventional mapping techniques, allowing a better description of the reservoir heterogeneity. Another advantage of geostatistics is that it can integrate different types of data independently measured at different scales. In this work, we show how the techniques mentioned above were applied in an integrated way to make the carbonate reservoir of Congro field economically viable. Team integration (geophysicist, geologist, geostatistician, reservoir engineer, drilling engineer, economist, etc.) was another key element to the success of this project. Pressured by time, the team did not take the conventional approach of taking one step at a time to build the reservoir model. That is, to build the geophysical model first, then the geological model, and, finally, build the numerical simulation model. Instead, the geophysicist, the geologist, and the reservoir engineer worked together so that their models were built almost simultaneously. This approach saved time and ensured that the models were coherent with all available data.

A Petrobras deepwater exploration well is planned to be drilled in water depth greater than 2438 m (8,000 ft) offshore Brazil. As is typical of deepwater wells, it has a narrow drilling window between pore pressure and fracture gradient, requiring many casing strings to reach total depth (TD). Because pressure-related problems are often extremely costly when drilling conventionally in deep water, initial design assumptions were conservative, assuming the maximum pore pressure and minimum fracture gradient for casing-point and pipe selection. As with all conventional casing designs, the resulting pipe has limited capacity to withstand increased burst and collapse loads associated with extending hole sections if the opportunity arises.Managed-pressure drilling (MPD) enables the development of an adaptive well design by providing three key advantages over conventional drilling: the ability to detect kicks and losses extremely accurately (in gallons, rather than barrels); the ability to rapidly respond to and dynamically control detected kicks and losses by adjusting backpressure on the annulus, keeping kick volumes small; and the ability to perform dynamic pore-pressure and formation-integrity tests. Detecting and responding rapidly to kicks allows for the well to be designed with smaller kick tolerances. Furthermore, by keeping the kicks small, they can be circulated out quickly without requiring conventional, time-consuming well-control operations, which often lead to further hole problems. When this advantage is coupled with dynamic pore-pressure tests and dynamic formation-integrity tests, real-time optimization of casing points can be achieved safely with reduced risk of costly well-control incidents.The method presented here, applicable to any deepwater well, uses low, expected, and high pore-pressure and fracture-gradient estimates to develop an adaptive casing design for the well. In this paper, kick-tolerance calculations for selecting casing points by use of MPD are defined. The effect of reduced kick-tolerance requirements because of the application of MPD is demonstrated, and an adaptive procedure for real-time design optimization of the well is presented. The method results in decision criteria that identify key depths where casing strings can be eliminated without compromising the ability to reach objective TD. The resulting adaptive casing design will most likely eliminate at least one, and has the potential to eliminate two, casing strings, representing significant cost savings.

Taquipe is one of the Petrobras operational bases for the oil exploration and production activities in Bahia. In order to develop its activities Taquipe uses large amounts of water, supplied through wells. The main consumption installations units are: garages, refectory and the drilling and completion fluid manufacturing plant (DCFMP). The aim of this article is to present a study about the use of rainwater as an alternative source for water supply in the DCFMP. The methodology used was divided into two stages. The first one was the construction of a hydric balance which was used to identify opportunities for optimising the water and effluent systems. The second stage was to conduct a study about one of these opportunities found: the use of rain water in the completion fluid manufacturing process. The amount of rain water available was determined by a hydrological study based in the precipitation historical registered in meteorological stations while its quality was found by a sample campaign. The samples were collected in points such as streets, gutters, canals and other drainage devices. The drainage basins inside the base and the runoff coefficients were also considered. The rain water quality was, then, compared to the water necessary for the completion fluid manufacturing process. Of the three drainage basins studied one was rejected because of the poor water quality. The critical parameters were Calcium, Bicarbonate and Hardness. A rain water system was designed, consisting of rain water reservoirs, pipelines and hydraulic pumps. This study represents a considerable advance in terms of the most modern principles about water resources. It will make possible to save 11344 cubic meters a year which represent 52% of water consumption in the completion fluid manufacturing process.