Shale hydration inhibition agent(s) and method of use

A water-based drilling fluid for use in drilling wells through a formation containing a shale which swells in the presence of water, the drilling fluid comprising:

• an aqueous based continuous phase;
• a weighting material;
• and
• a shale hydration inhibition agent (SHIA) selected from the group consisting of
• (a) propylamine derivatives having the formula:
• R—Y—(CH2)n—NH2
• wherein n=3;
• Y═O or N;
• R=one or more —CH3 groups or a morpholino group;
• (b) hydrogenated poly(propyleneimine) dendrimers (HPPID) having a core with the formula N(-A-N*)3 and branches with the formula —H2 or -(AN*H2)2
• wherein A=(CH2)3 and N* is the growth point where two additional branches are attached;
• and
• (c) polyamine twin dendrimers (PTD) having a core with the formula
• H2N—(CH2)x—NH2
• wherein 2≦x≦6, and branches B with the formula —(CH2—CH2—CH2—NH2), wherein the core and the branches are arranged as:
• (B)2n . . . —(B)8—(B)4—(B)2—[H2N—(CH2)x—NH2]—(B)2—(B)4—(B)8— . . . (B)2n
• wherein n is the dendrimer growth generation number and n<10;
• wherein the SHIA is present in a sufficient amount to reduce shale swelling.