An Integrated In-Situ Stress Measurement Program for Deepwater Brown Field Developments

Chan, A. W. (Shell Exploration and Production Company) | Cuttitta, M. (Shell Exploration and Production Company) | O´Reilly, G. (Shell Exploration and Production Company)

OnePetro 

ABSTRACT: The Mars field began production in the mid-1990s, and a wealth of direct and indirect stress measurements have been accumulated through drilling and completion operations over the years. Typical data collected over the years include casing shoe formation integrity tests, leak-off tests, lost circulation events while drilling, mini-frac during completions, and step-rate tests in the producing reservoirs. While this traditional dataset provides some basic insights into stress characterization around the basin, extrapolating these data for more specific operations can be challenging due to the complexity from various level of activities across the 70+ stacked sands. Some of the challenges in utilizing the traditional dataset includes defining waterflood injection limits and in managing drilling margin through severely depleted zones. To aid better decision making, some novel measurement programs have been conducted over the last few years such as cased-hole microfracture tests during abandonment of wellbores. More recently, a series of modified open-hole extended leak-off tests were conducted to define the impacts of drilling mud on fracture pressures where both depleted reservoir sands and bounding shales were exposed. These newly acquired data along with our traditional dataset provided the Mars asset new insights into the impacts of various operation decisions on fracturing potentials both in the caprock and through depleted reservoirs. This dataset also unlocked new reserves and opportunities within the basin. In this paper, we provide an overview on the various components of this unique in-situ stress measurement program that has significantly impacted both our development and operating philosophy at Mars.

1. INTRODUCTION

The Mars basin consists of over twenty major stacked reservoirs in the Deepwater Gulf of Mexico and has been on production since 1996. Despite waterflood commencing in 2005, struggles in achieving expected injection rate and well life from the early injectors has caused depletion in excess of 5,000 psi in several reservoirs. To continue developing some of the basin’s deeper and larger reservoirs, future wells must be drilled through many of these shallow depleted sands. If one of these reservoirs is overly depleted and can no longer be drilled safely, significant volumes from the deeper reservoirs could be lost. An integrated team consisting of subsurface specialists (petrophysicist, geologist, geomechanist, reservoir engineer, production technologist), drilling engineers, and economists have completed a field drillability study. This study evaluated the drilling margin, which is the difference between the expected pore pressure (PP) and estimated depleted fracture gradient (FG), for more than 70 proposed wells in the field development plan (FDP). Based on Shell’s understanding of depleted fracture gradients at the time, several planned wells were deemed un-drillable and many more would become un-drillable if reservoirs continued to deplete with no pressure maintenance. Without a successful waterflood program or depleted drilling program in place, the Mars asset opted to curtail production from specific reservoirs, which amounted to over 10,000 barrels of oil per day. Adjustments to the FDP to protect access to the deeper resources also caused a decrease in value of the asset. Meanwhile, the value of the waterflood program also diminished because of the need to continue replacing water injector wells, further delaying the blowdown. The asset recognized that the success of a challenging depleted drilling program along with an efficient waterflood program requires a thorough understanding of the subsurface stresses.

  Country: North America > United States (1.00)
  Industry: Energy > Oil & Gas > Upstream (1.00)
  Oilfield Places:
  Technology: Information Technology (0.68)