Most of the reservoirs located in the Campos Basin, deepwater and ultra-deepwater offshore Brazil are described as unconsolidated sandstone that require sand control on both producers and water injection wells. Horizontal Open Hole Gravel Pack completions are the preferred method of development. Due to the recent discoveries of heavy oil reservoirs, there is a necessity of longer horizontal open hole sections. Low fracture gradients may limit the length of gravel pack in the open hole section because of the pressure increase during the Beta wave proppant deposition phase.
This system allows the gravel pack assembly to be installed and the gravel pack to be pumped during the alpha and beta wave deposition phases without the limitation of high pressures that could fracture the well. The benefits of the Single Trip Horizontal Gravel Pack and Selective Stimulation System (SHGPSS) using the differential valve include the ability to complete longer horizontal intervals, valuable rig-time savings and, efficient mechanical diversion of the stimulation fluid.
This paper outlines the first application of the SHGPSS system using a differential valve to successfully complete a horizontal well in the Campos Basin, offshore Brazil. The need for a differential valve is primarily in horizontal gravel packing operations when normal circulating rates and pressures around the openhole would exceed formation break down pressure. The valve is intended to be easily spaced out and run in the washpipe. At a predetermined differential pressure the valve opens and the return flow path distance around the bottom of the tailpipe is shortened, thus reducing backpressure preventing filter cake damage without slowing the pump rate.
Economic considerations along with completion efficiencies are especially important on deepwater, subsea completions. The utilization of differential valves allows completion of extended-reach open hole wells and/or low fracture gradient reservoirs insuring alpha and beta wave proppant deposition phases yielding efficient completions with improved coverage.
Most oil and gas reserves in Campos Basin (Figure 1) are located in deepwater (300m – 1000m) and ultra-deepwater (greater than 1000m). Economics dictate field development and planning is the key for successful return on investment. Completion systems that can minimize rig time and future interventions are particularly important for deepwater and ultra-deepwater environments1. Economic development of deepwater projects demands that a minimum number of wells be drilled and still effectively drain the reservoir2.
The gravel packing of horizontal wells has been around for many years, but recently as we push the boundaries of economics, technology, and fracture gradients, the mechanisms needed to perform these tasks grow more complex. With an open hole gravel pack completion, the tool string is placed in the well prior to any filter cake removal to prevent fluid losses to the open hole section. This allows for reduced leak off which acts like a closed system in order to place proppant around sized screen to keep formation sand from entering the wellbore. The gravel pack slurry is pumped down the workstring and through the SHGPSS single trip crossover tool in the normal circulation pattern (Figure 2). Slurry is pumped down the work string and through the exit ports then in the annulus of the open hole and screen and returns of clean fluid are taken up the washpipe back to surface. The washpipe is sized in order to maintain the minimun accepted 0.803 ratio to allow for a small area between the washpipe and screen, diverting fluid out of the screen to avoid premature slurry dehydration, preventing a premature sandout. Gravel packing with low viscosity fluids allows for lower friction pressure in the system, which is a must for wells with a low frac gradient. As wells become longer and longer, the friction of circulating through the system is becoming enough to break down the formation and lose the filter cake. In extreme cases the friction of just circulating will break down the formation and fluid losses will occur, thus not achieving adequate proppant placement.