Session: 11-02-03 Well Drilling Fluids and Hydraulics -3

Paper Number: 79501

79501 - The Role of Particle Size Distribution for Fluid Loss Materials on Formation of Filter-Cakes and Avoiding Formation Damage 

Numerous studies have shown that careful particle size selection is the main parameter for reducing fluid loss when drilling permeable or fractured formations. These studies have been converted to industry practices in terms of designing fluids for specific drilling operations. The methods are generally built around either the D50 or D90 values of the particles in the fluid as a relative size to the pore openings of the formation, to minimise fluid loss, but with little consideration made to specifically limit formation damage.

A series of studies were conducted to measure fluid loss, solids invasion and formation damage. Further, it was developed a model for measuring the permeability changes caused by the internal- and external filter-cakes, and thereby isolating the permeabilities of the original formation, the temporary external filter-cake and the more permanent internal filter-cake.

It was found that the building of an effective internal filtercake was optimal with regards to reducing fluid loss and stabilizing the formation, but that this effect also correlated with more invasion of solids into the formation, and thereby often a larger formation damage.

It was discovered that different particle size methods should be used for optimising a fluid with regards to wellbore strengthening during the drilling of upper sections of a well than when a drilling fluid is optimized for reservoir drilling and preventing formation damage.

It was concluded that conventional particle size methods were found to be adequate for designing a fluid for wellbore strengthening purposes. This led to higher solids invasion and a more impermeable internal filter-cake. However, for optimisation of reservoir drilling fluids, a different particle size selection method was found to be more useful to prevent reservoir formation damage. This method involves selecting particles that are resistant towards shear-degradation and with a D90 particle size ⪞ 3/2 the pore size of the formation.

Presenting Author: Karl Ronny Klungtvedt EMC

Authors:

Karl Ronny Klungtvedt EMC
Arild Saasen University of Stavanger