Inventor: Michael H. Johnson

FIELD OF THE INVENTION

[0001] The field of the invention is methods of addressing fouling of screened openings in fracturing systems by screening fluids before pumping into a fracturing assembly.

BACKGROUND OF THE INVENTION

[0002] Typically pressures in the borehole are controlled with mud systems. The mud is treated at the surface when returning from the borehole with vibrating screens, cyclone separators and other filtration equipment before being pumped back into the borehole. The circulating mud can remove cuttings from milling operations, solids entering the mud from sloughing off from the borehole wall or many other circumstances. The filtration devices target a predetermined mesh size.

[0003] Fracturing can be accomplished in a variety of ways but one way is to use a series of two position sleeve valves actuated sequentially with progressively larger balls landed on seats of each sleeve. The sleeve is in an open position for fracturing and then is shifted to a screened position for subsequent screening of later production flow. The screened position of one sliding sleeve is used to flow through to deliver a bigger ball with flow through the open screened position. The flow that delivers the progressively larger balls to accomplish the treatment is a special formulation that can create solids or gels of a size large enough to create a clogging situation when trying to deliver the next ball with flow out through an open screened port. This could slow the process by lengthening the time to get the ball to the seat or it may foul the screened opening to such a degree that subsequent production into the string through the screened opening can be prevented. The present invention responds to this situation with a filtration system for the treatment fluid before being delivered downhole down to the same or smaller particle size that the particles in the mud are screened out. These and other aspects of the present invention will be more readily apparent to those skilled in the art from a review of the detailed description of the preferred embodiment and the associated drawing while recognizing that the full scope of the invention is to be determined by the appended claims.

SUMMARY OF THE INVENTION

[0004] Treatment fluid is screened at a surface location to the same particle size that the mud is screened before delivery into treating equipment in the borehole. Solids or microgels that can form are captured before pumping into the borehole to prevent fouling of screens designed to keep formation solids out of the produced fluids to the surface.

BRIEF DESCRIPTION OF THE DRAWING

[0005] Fig. 1 schematically illustrates the filtration of treating fluid at a surface location before pumping into the borehole.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0006] During well construction operations such as drilling, fracturing, and/or completion operations fluids are used which contain solids for weighting, such as drilling muds. Another example of fluids used are treating fluids such as polymer viscosifiers used to transport proppant or improve acid placement during reservoir stimulation.

[0007] There are instances where screens or filters at added in the well to prevent the proppant or formation sand from flowing back out of the well during production. These screens or filters can be run into the well during drilling or after drilling is completed. The screens or filters have a known range of opening sizes desired to prevent the flow of certain sand or proppant sizes during production operations of the reservoir.

[0008] Typically drilling mud is conditioned through a surface screening system of hydrocy clones and surface shaker screens to condition the mud to a particle size range that will not plug the screens or filters that are placed in the wellbore.

[0009] However, during stimulation operations such as fracturing or acidizing the fluids polymer viscosifiers are used which may be mixed in filtered fluids but once viscosified contain particles or microgels that yield larger particle sizes than are acceptable to prevent plugging of the screens or filters placed in the wellbore.

[0010] The present invention relates using a screen to ensure the particle size of any solids or microgels in the stimulation treating fluids are screened to the same particle sizes or less than the particle sizes achieved during screening of the drilling mud.

[0011] In the schematic diagram box 10 represents the mud mixing equipment that is then pumped with pumping equipment 12 and filtered to a predetermined particle size in filtration system 14. Some filtration can also take place with returning mud flow to the surface. The point being that the solids size that remains in the mud is smaller than a predetermined size to avoid screen fouling or clogging up small clearance spaces in the borehole.

[0012] Treatment fluids are mixed in blending system 16 and pumped by pumping system 18 and filtered in filtering system 20 to separate solids to the same or greater extent than in filtration system 14. It is the addition of the filtration system 20 that prevents clogging of screened openings 22 as will be described below.

[0013] Typically when treating with a series of sliding sleeves operated with a seated ball on a seat there are multiple positions for the sliding sleeve assembly 24. As illustrated, the screened opening 22 is aligned with opening to screen out solids from production after treating schematically represented by arrow 28. Prior to that the treatment happens when ports 30 are aligned with opening 26. Pressure on a seated ball on sleeve 24 shifts it to align screened opening 22 with opening 26. The ball that shifts the sleeve is blown through and the next ball for another sleeve uphole is pumped into the borehole using the screened opening 22 aligned to opening 26 as the path for pumping so that the next ball in sequence can be delivered with pumped treatment fluid. In the past pressure buildup on the inside of screened opening 22 has been noticed by surface personnel by virtue of an increase in surface pressure on the positive displacement pumps at the surface to move the desired fixed volume rate when delivering the next ball. The reason for this has been that solids formed in the treatment fluid mixture when introduced to the borehole have not been screened either at all or to the degree where they can pass through the screened opening 22. Deposition of such solids on the tubing side of screened openings 22 can embed in the screen and not only impede the treatment process by extending the time to deliver balls to seats but can also slow ultimate production flows when the well is put onto production. [0014] The present invention addresses this by filtration of treating fluids before introduction into the borehole to the same or greater degree than the filtration systems currently incorporated into mud circulating systems.

[0015] The teachings of the present disclosure may be used in a variety of well operations. These operations may involve using one or more treatment agents to treat a formation, the fluids resident in a formation, a wellbore, and / or equipment in the wellbore, such as production tubing. The treatment agents may be in the form of liquids, gases, solids, semi-solids, and mixtures thereof. Illustrative treatment agents include, but are not limited to, fracturing fluids, acids, steam, water, brine, anti-corrosion agents, cement, permeability modifiers, drilling muds, emulsifiers, demulsifiers, tracers, flow improvers etc. Illustrative well operations include, but are not limited to, hydraulic fracturing, stimulation, tracer injection, cleaning, acidizing, steam injection, water flooding, cementing, etc.

[0016] The above description is illustrative of the preferred embodiment and many modifications may be made by those skilled in the art without departing from the invention whose scope is to be determined from the literal and equivalent scope of the claims below: