Flowback Pre-treatment for Acid Stimulation in Tight Carbonate Wells
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Solution Overview
Problem
In water injection wells through tight carbonate reservoirs, acid treatments are less effective due to formation damage from drilling fluids and foreign matter, which reduces the permeability and flow rate, as hydrochloric acid cannot dissolve all damaging polymer components and pipe dope residues.
Innovation Solution
A pre-treatment flowback stage is introduced to remove undesirable materials from the wellbore and formation by controlling the flowback process using inherent reservoir pressure or nitrogen lift to reduce hydrostatic pressure, followed by standard acidizing procedures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If acid treatment is applied to water injection wells in tight carbonate formations, then the permeability and flow rate should be enhanced, but the effectiveness is seriously reduced due to formation damage from drilling fluids and foreign matter
Solution Approach 1:
The patent applies preliminary action by implementing a flowback step before acid treatment to remove drilling fluid filtrate, solids, and other damaging materials from the formation and wellbore. This preliminary cleaning action prepares the formation by eliminating the barrier materials that would otherwise prevent effective acid contact with the carbonate rock, thereby enabling subsequent acid treatment to achieve the desired permeability enhancement and injectivity improvement.
2Productivity
If hydrochloric acid is used to dissolve calcium carbonate minerals in filter cake and formation, then the permeability should be improved, but the acid is incapable of dissolving or degrading polymer components such as xanthan gum and starch
Solution Approach 1:
The patent applies the taking out principle by using the flowback step to extract and remove polymer-containing drilling fluid materials from the formation and wellbore before acid treatment. By removing these polymer components (xanthan gum, starch) that are resistant to acid dissolution, the patent prevents them from interfering with acid effectiveness, allowing the acid treatment to focus on dissolving calcium carbonate minerals and achieving the desired permeability improvement without polymer interference.
3Productivity
If the injection rate is increased to enhance acid treatment effectiveness, then the treatment efficiency improves, but the injection pressure increases
Solution Approach 1:
The patent applies preliminary action by implementing a flowback step before acid treatment to clear the formation and wellbore of damaging materials. This preliminary cleaning reduces the resistance to flow, creating a more favorable condition for acid injection. As a result, the acid treatment can be performed at lower injection pressures while maintaining effective injection rates, because the flow paths are already cleared of polymer and solid barriers that would otherwise require higher pressures to overcome.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method significantly enhances the effectiveness of acid treatments by reducing the presence of damaging materials, resulting in a more than 2-fold increase in injectivity at lower injection pressures compared to standard treatments.
Implementation Method 1
the flowback can be achieved as a result of the inherent reservoir pressure and once the application of pressure on the drilling fluid is discontinued at the surface, the formation fluids will flow into the open-hole bore with sufficient force to displace the introduced wellbore fluids back up through the vertical wellbore
Implementation Method 2
the wellbore fluid is displaced by the use of a 'nitrogen lift' process in which nitrogen gas is circulated through the production/injection conduit and into the wellbore to displace liquids and to thereby reduce the hydrostatic pressure created by the fluid column
Data Source
AI summary
A method for treating an open-hole horizontal water injection well in a tight reservoir rock formation to remove undesirable materials such as formation-damaging polymers and chemical residues from pipe dope from the formation surface and adjacent formation pores prior to an acidizing treatment includes maintaining the drilling fluid pressure on the injection zone to induce flowback of formation fluid which is produced at the wellhead located at the earth's surface, where it is monitored for a reduction in the undesirable materials. In the event that the formation pressure is insufficient to produce formation fluid flowback, a nitrogen-lift is introduced at a predetermined location in the adjacent vertical well that will reduce the drilling fluid pressure to induce production of formation fluid at the wellhead.