The Use of Well Strengthening for Coping with Losses During Precompletion Operations Prior to Horizontal Open Hole Gravel Pack in Campos Basin Deep Waters

Abstract

The use of the alpha and beta wave technique for a successful Horizontal Open Hole Gravel Pack is based upon a well without, or with minimum, losses. In this case, the gravel particles will be adequately carried to the expected point of deposition. So, in case of any mud losses, both while drilling the reservoir or during pre-completion operations, an efficient loss control method should be used, in order to allow the best packing of the screen with gravel particles. Besides a brief revision of current techniques, this paper details a well succeeded loss control strengthening operation, when water based drilling fluid was injected during the pre-completion operations of a production well with long horizontal section in Campos Basin. After the displacement of the water base drilling fluid 9,4 ppg by completion fluid (brine) 9,4 ppg, the well started to lose about 15 bph of fluid. Based upon solid previous experience, an acceptable limit for WBM losses is about 2 bph. The well was reconditioned with WBM, lowering the losses for 5 bph, still too high. So a LCM pill was injected into the formation, above fracture pressure, using the "sealing fracture method". This procedure resulted in a well without any losses, which allowed the displacement by brine, the running of premium screens and complete the pumping of HOHGP without any incidents. Introduction The need for high productivities and for the optimization of the rig time made the horizontal wells the pattern for drainage of Campos' Basin deep water reservoirs. The solid experience of 260 wells equipped with HOHGP, with more than 550000 feet of screens run in, without a single failure in contolling sand production, confirms the success of this choice. This success is the result of the great evolution of procedures that incorporated the lessons learned since the first horizontal gravel packed well built in 1998. The most important of these learned lessons is the perfect understanding of the process of alpha-beta waves for deposition of the gravel pack and its requirements, such as: a well without losses, a thin mud cake (without fluff) and with appropriate gravel granulometry, the knowledge of the operational limits imposed by the geo-mechanics conditions, etc. As the demanded high productivity depends a lot of a thin non-damaging mudcake and HOHGP depends on a well without any losses, a narrow operational window is left by pre-completions operations. Therefore, to understand both the wellbore losses and leak off importance in the gravel pack process is a key of the HOHGP success. By this way, managing losses become a natural part of the process. Some Basic Concepts Alpha-Beta Wave Fundamentals The alpha-beta wave technique is based upon the return rate. Although simulations (see graphs below) and technical descriptions normally refer to pumping rate or entrance velocity, what really matters is the output velocity, that means return rate.