Recent Advances in Deepwater Horizontal Injector Wells Acidizing in Campos Basin

Abstract

In most of its deepwater Campos Basin oilfields, Petrobras' strategy has been to develop the waterflooding systems by using open hole horizontal gravel packing. Both, perforation and gravel packing operations, are only possible by the presence of the filtercake, formed on the formation face during the drilling process. Nevertheless, that film becomes an impediment to injection and must be removed to obtain good injectivity. Despite the development of special tools that permit to acidize just after the gravel packing operation, there was still a need for reducing the operation time and to increase the damage removal efficiency. With this purpose, changes were made in the diverting systems to allow each acidizing stage to treat larger intervals, thus reducing the treatment's total number of stages. This improvement was possible by modeling the fluid flow through the tool's perforated extension, which saved 30% of the pumping time. Parallel to this development, acidizing historical data were revised and filtercake invasion studies were performed. The conclusion was that more aggressive acidizing formulations could be used, what reduced the pumping volume and reduced the job time even further, to about 50% of the previous times. Post job formation tests performed have shown that not only a job time reduction was achieved, but also, a better formation damage removal. The good effects observed have resulted in a general review in the design of the horizontal injectors acidizing jobs, improving the operation's safety, efficiency and effectiveness. This paper will describe the technique, job details and the results obtained for these particular operations. Introduction Horizontal open hole gravel packs have been used as Petrobras' main strategy for the development of deepwater fields. Although the producer wells have usually presented very good results since the beginning of its utilization, the water injectors have presented a substantially more complex challenge, once they need to be acidized to achieve good injectivities, despite the care taken during the drilling and completion phases. Besides the acidizing tool's development, that allow to perform the treatment in small isolated sections of the horizontal gravel pack just after the gravel packing, and the general acidizing pumping method improvement, there is still a need for reducing the operation time, what could be achieved by two approaches:Reducing the total pumping volumeExtending the treated area per stage Reduce the total pumping volume results in decreasing the treatment's dissolving power, what could induce a high residual damage. In the same way, a bigger treated area per stage could cause bad acid distribution and poor damage removal, due the difficulties to divert the treatment along a larger interval. To minimize those problems, studies involving the filter cake and filtrate / rock interaction were performed, allowing a better understanding of the damage mechanism. In parallel, studies regarding the diverting effects in larger intervals were performed to verify which were the dominant influences during the acidizing operations. The results of those researches have suggested the need for a great dissolving power, in order to improve the attack over the main damage area and, at the same time, to reduce the treatment volume. Also, it was achieved that the formation injectivity had the major influence over the diverting effects in a limited open hole section. In this manner, a significant reduction in the treatment volume and an increase in the HOHGP's treated area per acid stage were possible, resulting in a 30% reduction in the pumping time, without sacrificing the damage removal.

Evaluation of chemical and mechanical resistance of virgin and recycled poly (ethylene terephthalate) and poly(methylene oxide) when applied as gravel pack in petroleum wells

“…Exposure periods were chosen considering the maximum exposure time expected during chemical treatments usually performed in wells [7,8] : 24 h for acid and solvents mixture and 96 h for Trilon CK. After the exposure period, the samples were washed with neutral detergent and running water onto a metal sieve of 250μm Mesh size (thin enough to avoid significant loss of polymer fragments) vacuum dried at 70 °C for 24 h, and then weighed.…”

A New Acid Treatment Procedure to Improve Injectivity in Brazil Offshore Horizontal Wells

“…In traditional acidizing jobs performed in Campos and Espirito Santo Basins, treatments were pumped through 2 or 3 screens joints (24 or 35 m). As described in Pereira et al, 2007, after increasing the treated interval extension from 2 or 3 screens joints to 5 screens joints (60 m), a significant reduction in the treatment time was observed, without great differences in damage removal.…”