Results in Construction and Completion for Extend-Instrumented Horizontal Wells Into Low-Pressure Zone: Case History—Reservoir Miocene Ll-03, Maracaibo Lake Venezuela

Abstract

One of old and most important West Venezuelan Oil fields is the LL-03 reservoir which has accumulated more than 1200 MMBN and actually represent the 30% medium oil daily production of Exploitation Unit "La Salina", Maracaibo District, PDVSA. This reservoir is characterized for contain 30% of shale with not consolidated sand at low pressure with 450 psi at 3500 feet of depth with interleayer of clay and high permeability with lost of severe circulation risks, in order to develop the reserves of 24° API oil it was designed and execute the secondary recovery project called Fase IV through instrumented horizontal wells into low-pressure zone. Due the depleted conditions of this reservoir it was begun the search of new alternatives for perforation fluids competitive at technical and economic levels, being one of the main challenges to ensure the success in the construction and completion for extend horizontal wells. After obtained the formulation of the optimal fluid to use it was come to design the directional plan and the mechanical completion for sand control, being considered in addition the use of permanent downhole gauge for pressure and temperature readings, conforming therefore the instrumented well. The stability of the system, the effectiveness of the saline seal and operational practice allowed the successful perforation of 3 instrumented horizontal wells (2 injectors and 1 producer) with the formulated saline fluid in a horizontal section of 2699 feet average without observe hole instability problems having completed the wells with mesh screen for sand control and permanent downhole gauge for pressure and temperature readings in a concentric string, after removing the filter cake generated by the perforating fluid it was obtained 22 months of continuous and stable production of 900 BNPD results Vs 450 BPPD expected for PB-763 well, opening opportunities for the perforation of 3 wells in similar conditions and it was begun the project for perforation of the first multilateral well in this same reservoir. INTRODUCTION The reservoir LL-03 of the Miocene from the Rosa Mediano field after 50 years of production maintains reserves surpluses in the order of the 340 MMBN with pressure levels that oscillate between 300 – 600 psi, reason why the drilling has been associated to the risk of lost of circulation. In order to increase the area of drainage in wells drilled in the LR-60 sand of this field, it was begun the construction of horizontal wells making an investigation of the fluid to use to maintain the stability of the hole in the whole horizontal section of production during the drilling, selecting water based system of "aphrons" obtaining excellent operational results allowing the construction and completion of the well, but unsuccessful production level due to the low obtained initial production, reason to perform a chemical treatment for the removal of the damage created by the filter cake generated by perforation fluids obtaining an initial production of 1300 BPD, which was lower than the expected potential. This field has been put under projects of secondary recovery by water injection to maintain the production present of the reservoir, such has been implanted from year 1979 with the construction of vertical wells, denominated Phase I, the second and third project called Phase II and Phase III with peripheral geometric adjustments of seven inverted points and beginning the injection from year 1985, next to this is made an extension of Phase I in 1999. Later to these advances of secondary recovery it was performed a study of simulation made to the LL-03 reservoir from year 2000, being created a new project of secondary recovery denominated Phase IV, which would have a horizontal well adjustment of extended arm (over 1000 feet of length in the horizontal section of production/injection), expecting to recover 70.48 MMBNP. In order to obtain the objective of this project it was made an investigation of the type of drilling fluid to use, initiating the study with the obtained experience years back with another system of fluid, the same one was evaluated technically and economically against other systems being very competitive, in addition it had to be of easy removal to satisfy the volumetric success.