A method includes adding a clay to water to form a suspension of clay in water, the clay including pieces of clay having an average diameter of at least 2 μm; adding a dispersant to the suspension of clay in water to form a drilling fluid; and injecting the drilling fluid into a well. In the drilling fluid, the dispersant interacts with the clay to form nanoscale particles of clay having an average diameter of less than 500 nm.

Techniques for drilling wellbores are described. The techniques include a) introducing a drilling fluid composition into a borehole defined by a formation; b) introducing a thinner composition including at least one tannin and at least one metal salt into the borehole; and c) contacting the thinner composition and the drilling fluid composition in the borehole, wherein the at least one tannin and at least one metal salt are not complexed ex situ. The at least one metal salt includes at least one copper salt, at least one zinc salt, or both at least one copper salt and at least one zinc salt.

A method of treating a well that includes introducing a well treatment fluid into the well, and a well treatment fluid, are provided. The well treatment fluid comprises an aqueous base fluid, a bridging agent, a viscosifying agent, and a water soluble, biodegradable graft copolymer. In one embodiment, for example, the method is a method of cementing a casing in a well. In this embodiment, the well treatment fluid is a cement spacer fluid.

Techniques for drilling wellbores are described. The techniques include a) introducing a drilling fluid composition into a borehole defined by a formation; b) introducing a thinner composition including at least one tannin and at least one metal salt into the borehole; and c) contacting the thinner composition and the drilling fluid composition in the borehole, wherein the at least one tannin and at least one metal salt are not complexed ex situ. The at least one metal salt includes at least one copper salt, at least one zinc salt, or both at least one copper salt and at least one zinc salt.

A method for drilling a tunnel through a formation must address environmental concerns. One tunneling method comprises the steps of: preparing a mixed metal-viscosified drilling fluid including bentonite, a mixed metal viscosifier and controlling pH to 8.5 to 9.5 to permit a reaction between the bentonite and the mixed metal viscosifier; adding at least one of: (i) calcium sulfate and (ii) a potassium salt; and pumping the drilling fluid while drilling the tunnel with the pH lowered to 7-9. The amount of mixed metal viscosifier used can be limited such that the weight ratio of mixed metal viscosifier to MBT reaches up to 1:30. In the event that there is a problematic increase in viscosity, a non-toxic anionic thinner can be added to the drilling fluid. One such anionic thinner is a polyacrylate.

A method of treating a well that includes introducing a well treatment fluid into the well, and a well treatment fluid, are provided. The well treatment fluid comprises an aqueous base fluid, a bridging agent, a viscosifying agent, and a water soluble, biodegradable graft copolymer. In one embodiment, for example, the method is a method of cementing a casing in a well. In this embodiment, the well treatment fluid is a cement spacer fluid.

Techniques for drilling wellbores are described. The techniques include a) introducing a drilling fluid composition into a borehole defined by a formation; b) introducing a thinner composition including at least one tannin and at least one metal salt into the borehole; and c) contacting the thinner composition and the drilling fluid composition in the borehole, wherein the at least one tannin and at least one metal salt are not complexed ex situ. The at least one metal salt includes at least one copper salt, at least one zinc salt, or both at least one copper salt and at least one zinc salt.

The present disclosure discloses a modified nano-silica plugging agent, a water-based drilling fluid, and a preparation method and use thereof.

Techniques for drilling wellbores are described. The techniques include a) introducing a drilling fluid composition into a borehole defined by a formation; b) introducing a thinner composition including at least one tannin and at least one metal salt into the borehole; and c) contacting the thinner composition and the drilling fluid composition in the borehole, wherein the at least one tannin and at least one metal salt are not complexed ex situ. The at least one metal salt includes at least one copper salt, at least one zinc salt, or both at least one copper salt and at least one zinc salt.

A date tree trunk- and rachis-based lost circulation material (LCM) is provided. The date tree trunk and rachis LCM includes superfine date tree trunk fibers produced from date tree trunks and superfine date tree rachis fibers produced from date tree rachises. The date tree trunks and rachises may be obtained from the date tree waste produced by the processing of date trees in the production of date fruits. The date tree trunk and rachis LCM may include fibers having lengths in the range of about 20 microns to about 300 microns. Methods of lost circulation control using a date tree trunk and rachis LCM and manufacture of a date tree trunk and rachis LCM are also provided.